I've encountered bugs that are extremely difficult to reproduce reliably and/or explain definitively, but that appear to be solved. When this happens, how much time should I spend chasing it down?
Example: this SO question and this related jQuery forum post, which offer differing solutions. The issue was reproducible intermittently until the change I discuss in the SO question, and not at all after the change.
If I don't conclusively understand what caused the bug, can I claim with confidence that it won't come back in the future by surprise?