The same occurs if I start jammr when using the external monitor, and then I switch to the laptop screen.
So far, the only way I found to restore normal operation is Ctrl-C in the xterm and restart jammr.
I don't get any messages in the xterm window, but I get the following messages in ~/.local/share/jammr/jammr/log.txt as soon as I switch to the external monitor:
Jun 12 2015 22:08:14 WARN: QPainter::begin: Paint device returned engine == 0, type: 2 Jun 12 2015 22:08:14 WARN: QPainter::end: Painter not active, aborted Jun 12 2015 22:08:14 WARN: QPainter::begin: Paint device returned engine == 0, type: 2 Jun 12 2015 22:08:14 WARN: QPainter::end: Painter not active, aborted Jun 12 2015 22:08:14 WARN: QPainter::begin: Paint device returned engine == 0, type: 2 Jun 12 2015 22:08:14 WARN: QPainter::end: Painter not active, aborted Jun 12 2015 22:08:14 WARN: QPainter::begin: Paint device returned engine == 0, type: 2 Jun 12 2015 22:08:14 WARN: QPainter::end: Painter not active, aborted Jun 12 2015 22:08:14 WARN: QPainter::begin: Paint device returned engine == 0, type: 2 Jun 12 2015 22:08:14 WARN: QPainter::end: Painter not active, aborted Jun 12 2015 22:08:14 WARN: QBackingStore::flush() called for QWidgetWindow(0x9844ff0, name = "MainWindowClassWindow") which does not have a handle. Jun 12 2015 22:08:14 WARN: QPainter::begin: Paint device returned engine == 0, type: 2 Jun 12 2015 22:08:14 WARN: QBackingStore::flush() called for QWidgetWindow(0x9918530, name = "JammrConnectDialogClassWindow") which does not have a handle. Jun 12 2015 22:08:15 WARN: QBackingStore::flush() called for QWidgetWindow(0x9918530, name = "JammrConnectDialogClassWindow") which does not have a handle.
Hope this helps! If you think this is a bug and need extra testing to debug, just let me know and I'll be glad to help!