I have noticed this happen a lot. Lucky there is the undo button.
I am in artist view with a search. Have for example 4 albums showing in the bottom. I select/highlight the songs on two of the albums . I change the comment tags on those.
The songs are still highlighted, I click to change the year...It changes the year on everything in the bottom window, Not just the highlighted ones.
This is what happened:
After the comment tag was changed, the songs I chose are still highlighted. but in the tag action window it had changed to selecting everything in the bottom view.
This has happened numerous times, I have caught it some of the times. The undo only seems to go back one time. I have had to restore some music because of this.
If you were not using search, this could change your whole collection.
I would like to add that this does not happen every time, I am still trying to figure out what causes it.