This happens to me as well on 15.10 with the latest updates:
Linux 4.2.0-30-generic #35-Ubuntu SMP
Compiz 0.9.12.2+15.10.2015-0ubuntu1 Unity 7.3.3+15.10.2015-0ubuntu1
Hitting "alt-enter" gets me back as a work-around when clicking fails, but this has been a problem for a few versions of Ubuntu.
This happens to me as well on 15.10 with the latest updates:
Linux 4.2.0-30-generic #35-Ubuntu SMP
Compiz 0.9.12. 2+15.10. 2015-0ubuntu1 10.2015- 0ubuntu1
Unity 7.3.3+15.
Hitting "alt-enter" gets me back as a work-around when clicking fails, but this has been a problem for a few versions of Ubuntu.