Initial opening of ComboBox takes extremely long in IE11

Hi,
we have a ComboBox with 2 entries, the first of them is the empty NullSelection-Item, the second one is an example entry.
After clearing the IE11 cache and loading the application, when I open the ComboBox entries, the server communication takes extremely long. The entries of the option list are being loaded from a database before the UI initialization.

In the debug log below, the “resize” request takes around 70s while other server requests complete relatively fast.

Is this an IE bug?
Are there possibilities to implement a workaround?

Thanks a lot

Environment:
Java 7
vaadin 7.6.8
IE 11.0.9600.18665

413msStarting layout phase
421msMeasured 11 non connector elements
439msPass 1 measured 44 elements, fired 0 listeners and did 7 layouts.
505msPass 2 measured 18 elements, fired 0 listeners and did 2 layouts.
567msPass 3 measured 3 elements, fired 0 listeners and did 2 layouts.
570msPass 4 measured 2 elements, fired 0 listeners and did 1 layouts.
577msDid overflow fix for 1 elements
585msPass 5 measured 2 elements, fired 0 listeners and did 0 layouts.
594msDid overflow fix for 2 elements
604msPass 6 measured 3 elements, fired 0 listeners and did 0 layouts.
605msNo more changes in pass 7
633msTotal layout phase time: 220ms
633ms * Dumping state changes to the console
634msUIDL: undefined
705msFirst response processed 1895 ms after fetchStart
705ms Processing time was 579ms
706msReferenced paintables: 37
720msStarting layout phase
724msMeasured 11 non connector elements
728msPass 1 measured 1 elements, fired 0 listeners and did 3 layouts.
788msPass 2 measured 3 elements, fired 0 listeners and did 1 layouts.
792msPass 3 measured 2 elements, fired 0 listeners and did 1 layouts.
799msDid overflow fix for 1 elements
808msPass 4 measured 2 elements, fired 0 listeners and did 1 layouts.
810msPass 5 measured 1 elements, fired 0 listeners and did 0 layouts.
822msDid overflow fix for 2 elements
831msPass 6 measured 3 elements, fired 0 listeners and did 0 layouts.
832msNo more changes in pass 7
832msTotal layout phase time: 112ms
2819msRPC invocations to be sent to the server:
2820ms   657 (class com.vaadin.client.ui.ui.UIConnector) :
2822ms      com.vaadin.shared.ui.ui.UIServerRpc.resize([731, 1600, 1600, 731]
)
2823ms   673 (class com.vaadin.client.ui.combobox.ComboBoxConnector) :
2824ms      v.v(filter : )
2825ms      v.v(page : -1)
[u]
[b]
2829msSending xhr message to server: {"csrfToken":"2ccd66d6-2214-4382-aeaf-8251339219f6","rpc":[["657","com.vaadin.shared.ui.ui.UIServerRpc","resize",[731,1600,1600,731]
],["673","v","v",["filter",["s",""]
]],["673","v","v",["page",["i",-1]
]]],"syncId":0,"clientId":0,"wsver":"7.6.8"}
72992ms Server visit took 70162.867ms
[/b]
[/u]
72994msJSON parsing took 0.107ms
72994msReceived xhr message: for(;;);[{"syncId": 1, "clientId": 1, "changes" : [["change",{"pid":"673"},["4",{"id":"673","prompt":"Koll.-Prog. auswählen","nullselect":true,"pagelength":0,"filteringmode":"STARTSWITH","totalitems":2,"totalMatches":2,"v":{"selected":[]
,"filter":"","page":0}},["options",{},["so",{"caption":"","key":""}]
,["so",{"caption":"test","key":"1"}]
]]]], "state":{}, "types":{"673":"4"}, "hierarchy":{"673":[]}, "rpc" : []
, "meta" : {}, "resources" : {}, "timings":[832, 2]
}]
72995msHandling message from server
72996ms * Handling resources from server
72997ms * Handling type inheritance map from server
72998msHandling type mappings from server
72998msHandling resource dependencies
72999ms * Handling meta information
73000ms * Creating connectors (if needed)
73000ms * Updating connector states
73001ms * Handling locales
73002ms * Updating connector hierarchy
73003ms * Running @DelegateToWidget
73004ms * Sending state change events
73005ms * Passing UIDL to Vaadin 6 style connectors
73017ms * Performing server to client RPC calls
73018ms* Unregistered 0 connectors
73018mshandleUIDLMessage: 18 ms
73019msStarting layout phase
73026msMeasured 11 non connector elements
73037msPass 1 measured 21 elements, fired 0 listeners and did 1 layouts.
73046msDid overflow fix for 1 elements
73055msPass 2 measured 2 elements, fired 0 listeners and did 0 layouts.
73055msNo more changes in pass 3
73056msTotal layout phase time: 36ms
73056ms * Dumping state changes to the console
73057msUIDL: undefined
73059ms Processing time was 64ms
73059msReferenced paintables: 37
73060msRPC invocations to be sent to the server:
73060ms   673 (class com.vaadin.client.ui.combobox.ComboBoxConnector) :
73061ms      v.v(filter : )
73061ms      v.v(page : 0)
73062msSending xhr message to server: {"csrfToken":"2ccd66d6-2214-4382-aeaf-8251339219f6","rpc":[["673","v","v",["filter",["s",""]
]],["673","v","v",["page",["i",0]
]]],"syncId":1,"clientId":1}
73286msServer visit took 224.141ms
73288msJSON parsing took 0.069ms
73288msReceived xhr message: for(;;);[{"syncId": 2, "clientId": 2, "changes" : [["change",{"pid":"673"},["4",{"id":"673","prompt":"Koll.-Prog. auswählen","nullselect":true,"pagelength":0,"filteringmode":"STARTSWITH","totalitems":2,"totalMatches":2,"v":{"selected":[]
,"filter":"","page":0}},["options",{},["so",{"caption":"","key":""}]
,["so",{"caption":"test","key":"1"}]
]]]], "state":{}, "types":{"673":"4"}, "hierarchy":{"673":[]}, "rpc" : []
, "meta" : {}, "resources" : {}, "timings":[833, 1]
}]
73289msHandling message from server
73289ms * Handling resources from server
73289ms * Handling type inheritance map from server
73290msHandling type mappings from server
73290msHandling resource dependencies
73290ms * Handling meta information
73291ms * Creating connectors (if needed)
73291ms * Updating connector states
73291ms * Handling locales
73292ms * Updating connector hierarchy
73292ms * Running @DelegateToWidget
73292ms * Sending state change events
73293ms * Passing UIDL to Vaadin 6 style connectors
73300ms * Performing server to client RPC calls
73301ms* Unregistered 0 connectors
73301mshandleUIDLMessage: 10 ms
73301msStarting layout phase
73311msMeasured 11 non connector elements
73318msPass 1 measured 21 elements, fired 0 listeners and did 0 layouts.
73319msNo more changes in pass 2
73319msTotal layout phase time: 17ms
73320ms * Dumping state changes to the console
73320msUIDL: undefined
73322ms Processing time was 34ms
73322msReferenced paintables: 37