I heard a thing the other day I haven't heard for a long time. "That is not my code"
I believe no code and all code in your current project is Yours. There is nothing like finding a bug and leaving it be. If you can't correct it, flag it. Either in a bug tracking system, to the person currently working with that part or to wherever your project stores possible riscs.
This my code-your code mentality mentioned above lead to the bug being forgotten.
That is not considered good.