The problem is fixed. I just found that there is this in POE's Tk Loop for Active State Perl:

$_handle_poller = $poe_main_window->after(100, [\&_poll_for_io]);

This basicaly handles events while Tk is idle, which explains everything... All I did is I've changed the after time:

$_handle_poller = $poe_main_window->after(1, [\&_poll_for_io]);

Now I have no delays of any kind... my server is responding to my client immediately. Please don't hesitate to contact me for more information on this issue. As a conclusion I would like to recommend POE for proper Server-Client application on top of Tk. The things POE does is just pure magic. I personaly think that POE rocks!
Keep the good work Rocco!!
Anyway, Thank you all for the time and the suggestions!!