Vaadin 7.2.2 Push (avoid session memory leaks)

Vaadin 6 / 7 / 8
1

Hello. How to correctly to close session with Push enabled ?
I did
VaadinSession.Close()
 and http session rly is invalidate, but
VaadinSession.class
 instance still in heap.
And count of instances is incrasing even if i call gc. In last test count had been 2k+ and awaiting threads around 6k+.
Mb I’m doing something wrong. Or Vaadin has memory leak with push.