I haven't been able to recreate the exact circumstances, but here is what I know:
several albums will be loaded
I use Ctrl+A to select all tracks
I use the toolbar button to execute my actions groups
Occasionally, I will see "Applying actions to file... x of y" when I have less than y number of files loaded. This will result into data from one album being applied to another.
I'll post the extact steps if I can pinpoint them, sorry I don't have more information.
Actually- that's a very common occurance. I will frequently use the web source to get a cover or just the year and then cancel. I've done this for a long time and only noticed the issue with the latest version.
I've since reverted back to 2.37a and haven't seen a recurrence.