I just installed and run dosbox on my Ubuntu 16.04 machine, and I noticed that the shift keys don't work at all inside dosbox. They don't work in combination with any other key. If I hold shift and press and other button (say a letter key, or the semi-colon/colon key which I really really need for obvious reasons) nothing is printed out. I also tried building dosbox from the latest svn source code (obtained from the github mirror), but the problem persisted. The Ubuntu version of dosbox is 0.74.
This happens consistently and I've found no workarounds. I tried the keymapper but there didn't seem to be anything I could do there to fix my problem.