Plans can become disabled when branch name is different to source branch

Steps to reproduce:
1) Create a plan branch named after a git branch that it is tracking (eg both named branch-1)
2) Disable all the automatic cleanup for that branch
3) Change your plan branch source to another git branch (eg branch-2)
4) Delete the original branch in git (delete branch-1)

The bamboo branch now disables itself as it thinks its source branch is gone.