While developing (either features or bug fixes) I sometimes happen to discover bugs that are not directly related to what I'm working on. What should I do in that situation. Just fix it? Try to remember to fix it later? Write it down somewhere? Or enter it into the bug tracking system?

I generally enter it into the bug tracking system and let the process play itself out (i.e. triaging, assigning, etc.). However I have hardly ever seen another developer enter a bug. (Why is that?)