This indicates that something unusual happened on that page that the system thinks we need to know about.
We're committed to increasing the quality of our software, so we're constantly implementing new checks and stricter language features. So in almost every case, the "bug" is just the system letting us know that it found something that isn't technically wrong, but could be better. But sometimes, it's a real bug. Either way, we'll be automatically notified, and we'll check it out and fix it.
Most of the time, you can ignore the icon. But if you see one, it's a good indication to double check that everything happened as you expect.