This question is related, but about 12.04: Alt+Tab doesn't work when Citrix is in full screen
I am using citrix 13.1 xenapp on Kubuntu 14.04, and the suggestions in that post don't work in this configuration.
I am unable to get alt-tab window switching working. I use an additional monitor docked to my laptop. Hence, I configure the xenapp session window size to the size of the external monitor (1920x1080). I have configured it using settings option in browser (after logging-in).
If I change the layout from 'custom dimensions' to 'fullscreen', alt-tab works. However, it then occupies all of the screen space, including the laptop's.