I'm writing app with few threads. Main thread contains GUI, second thread is using QSerialDevice library to work with serial port. Everything seems to works fine but there is one issue. When I click on window bar and hold it longer than 3 seconds (or start to move window on the screen), second thread stops reading from serial port. After mouse release second thread resume serial port read/write.
Both thread are connected with signal-slot mechanism and all connections are defined with Qt::QueuedConnection flag.

Question: why GUI thread (main thread) is freezing background thread?

PS: I'm testing it on windows 7, qt 4.7.4.