Sounds like a crash is occurring, and we have indeed encountered a few reports like this.
To proceed with finding out which crash this is, please:
1. Apply the workaround from bug 994921.
2. Reproduce the crash.
3. Look in /var/crash for crash files and run: ubuntu-bug /var/crash/YOURFILE.crash
4. Tell us here the ID of the new bug created.
Sounds like a crash is occurring, and we have indeed encountered a few reports like this.
To proceed with finding out which crash this is, please:
1. Apply the workaround from bug 994921.
2. Reproduce the crash.
3. Look in /var/crash for crash files and run: YOURFILE. crash
ubuntu-bug /var/crash/
4. Tell us here the ID of the new bug created.