Redmine

Working on a custom implementation of RedMine, we found that if the user tries to change the tracker of a issue but do not save the modifications after all, custom values that belongs to the old tracker, but not to the new one, are removed. No history neither.

1. create tracker 1 with custom field A
2. create tracker 2 with custom field B
3. create an issue with tracker 1, assign a value to custom field A
4. edit the issue
5. change tracker to tracker 2
6. DO NOT SAVE and refresh the page
   custom field A is empty

The attached patch worked for us, it needs some testing though
I'm testing in redmine-1.1.1 but the code looks the same in newer versions