The cause of this
BugPattern is
CloneAndModifyProgramming.
What's the etymology of the bug?
Briefly, you 'reuse' code by copy and paste several times (the 'tiles'), find a bug in the code, and fix it in most but not all of the copies (leaving one or more 'rogue tiles'). The symptoms: A bug that was supposedly fixed shows up again (and again) in different usages. The solution: Refactor out the common code, so that there's only one 'tile'.
CategoryBug