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?
Un-Explainable Bugs?
bug;debugging
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?No. So your next question should be: how bad will it be if it does come back by surprise?If the answer is pretty bad, it will cost us millions of dollars and customers then you need to spend some time figuring it out. Best approach is to take a test environment and revert the change that you think fixed it and nothing else.If the answer is well, it'll be a bit embarrassing, but nothing we can't deal with then call it a glitch for now.