So, I just discovered that BOINC has a maximum estimated time remaining that the BOINC Manager will report. That maximum happens to be 87600 hours, which works out to exactly 10 years. So if you're running a WU that will take longer than 10 years to complete, BOINC won't be able to give you an accurate estimate as to how much time you have left.

Story:
Running a BURP WU. It's been running for 176+ hours, and the progress is stuck at 0.197% (which is normal, as the progress bar is meaningless on BURP). BOINC freaks out and the estimated time remaining skyrockets, and apparently maxes out at 87600 hours. Never thought I'd see that, so I had to share.