great developers with with bad process, quick turnaround, lack of ownership and bad habits can lead to a mess.

Also - maybe they inherited the code from a startup and never had the chance to refactor and so there was a mess from the start.

Either way, bugs happen. Of all kinds, even bad ones'.

More circumspect than a 'bug' is that this got through their tests. Their end-to-end testing should have picked this up.