Hello Edmundas,
Please create the most minimal sample application you can, with the two type of UserControls as you suggest, and send it to Support [at] VisualWebGui [dot] com with a link to this forum thread.
One user control that demonstrates the problem and one on which it does not occur.
Please also clean the solution before compressing it and reply to this post after sending, with the subject of the e-mail you send, so I would know to check for your support request.
Regards,
Ori Cohen
Support Manager, the Visual WebGui team