Hi @Attic
1) Is this a known problem?No, and it is hard to tell why the operation failed. If you have a stable way to reproduce it, we will fix it.
How do I avoid it when changing data types?
3) Whats the best way to recover my datatype? (As it does not show up in the backend.)
Remove the field from the meta data file, restart the website and try to add it again. Or you can add that field to the database manually