Change of flexform definition leads to duplicate data
We made some rearrangements in a fairly large flexform with several tabs. The main change was that some fields were moved into different tabs for improved usability.
It was clear that this would be problematic for existing content elements as the data for the moved fields would be lost. But after manually updating + saving such existing flexforms, it turned out that old data for the moved fields would remain in its original location, while also being saved to the new location.
So let's say field 'xyz' was moved from tab 'A' to tab 'B'. After opening and saving an existing flexform, you would now have data for 'xyz' in tab 'A' in tab 'B'.
I guess in real life this will probably not cause many problems as you would fetch data for a particular field from the location you'd expect it to be according to the flexform definition. But still: I don't see a legitimate reason why this should be the intended behaviour. The saved data should reflect the current definition of a flexform and not be a mixture of old and new, with zombie data floating around in your data structure.