TreeTable: expand/collapse icon disappears after hiding columns

Hi,
I'm having a problem using treeTable: I set the second column ("Title") as Hierarchy Column of a three columns table ("Code", "Title", "Value").

When I hide the columns before the chosen hierarchy column (the first column "Code" in my example) the hierarchy property is transferred to the following ones and it's even lost when hiding the other columns.

This behavior can be tested also in TreeTable official Demo http://demo.vaadin.com/treetable/WorkLog
STEPS:
1) drag column "LASTMODIFIED"  and drop it before column "NAME" (image 'TreeTable2.png')
2) hide column "LASTMODIFIED" (image 'TreeTable3.png')
3) hide column "HOURSDONE" (image 'TreeTable4.png')

After step 2 NAME is no more the hierarchy column, and this is an unwanted behavior.
After step3 expand/collapse icon disappears.

Can Anyone help me?
Thanks in advance