Server Push - Thread amount increase

Vaadin 6 / 7 / 8
1

Hello,
with Firefox, if Push is enabled, each time the Refresh button of the navigator is hit or after an application logout:


   getSession().close();
   getPage().setLocation("");

a new Thread is created in the Threadpool. After a while, the server needs to be restarted to avoid crashing.
(If the Push annotation is omitted, everything works fine as the number of threads does not increase.)

Am I missing a point or is this a bug?