If I replicate the issue on that thread, trying to edit submissions reproduces the issue on this thread about the “Start tag…”. Hopefully resolving formpack#303 will fix both cases.
For me, it seems related to #3751… Your “solutiion” with download/upload indicates that some difference against direcly editing makes the turn.
Sorry, from a user regard, it is confusing and a bit strange that different (parsing/converting) tools are working in the background and create such problems, esp. after an update.