Threads Tapestry 5.3.8 vs 5.4.3

I've got an issue/question regarding threads in tapesty.

We have application that is using tapestry. When we updated from 5.3.8 to
5.4.3 I've found that ajax request are not handled in separate thread.

For example: I have a long process that was executed in controller/class.
However, I've got also a JS script that is generating ajax request for a
component. In Tapestry 5.3.8 those request were handeled normaly. When I
switch to 5.4.3 my request are not handeled, unitl my main process from
controller ends.

Does anyone know something regarding this behaviour?

-- 
pozdrawiam

Michał Więckowski