qt33 threading issue after 5.3->5.4

[Kyryll A Mirnenko]

Having qt33 installed from recent ports working failless I've got 
upgraded 5.3 base to 5.4.
After that all threaded qt applications (`kmail`, `uic`, `gwenview`, 
etc.) fail to start saying:

Mutex init failed

Plz, give any ideas about fixing it - 'cause I'm totally confused about 
the reason of the issue -
if neither pthread API nor its internal logics has changed between 5.3 & 
5.4 what makes it
fail?