Hi Mats, I believe I have an understanding about why. Now, this is all based on supposition, so basically I am guessing. When you save a file in v5 or v4, they will be named as being generated in v4 or v5 in the meta data. The undo history is tied, I think, to the cache folder inside the song folder. As there is no history for edits done inside v5, there are no undo levels. This leads me to believe that all edit history is tied somewhere like the cache folder inside the song folder. Again I could be wrong. I hope that helps.