It would seem your old MM3 DB wasn't upgraded. Did you see a database upgrade message on first run of MediaMonkey 4? If not you may want to copy the MM3 database to the MM4 database location: http://www.mediamonkey.com/support/index.php?_m=knowledgebase&_a=viewarticle&kbarticleid=17

I also suggest disabling Infer Track Properties under Tools > Options > Library

and it would seem tag changes haven't been saved to the file. Either because you disabled this or because MediaMonkey doesn't have rights to do so. The Files to Edit > Unsynchronized Tags node can be used to identify tracks for whom the tag changes haven't been saved back to the files. (Make sure you're using this on your old MM3 database with the correct values).

Last week I installed the new MM version 4.02.1462 under Win7 Prof.
It was a very big NEGATIVE suprise to see that I had to change hundreds of records in my database after starting up the new release:
From ALL songtitles and ALL artist names starting with a figure 0-9) the figurs were lost!!!
for example:
25 minutes to go (Johnny Cash) was changed in: minutes to go
2 Brothers on the First Floor was changed in: Brothers on the First Floor