@DaveR Good morning. Sorry about the issue, this is happening because there are some or a particular music file that has that name written in lower case, and Poweramp is treating every other name that matches the character as same, even the ones with upper-case, and this is stored in Poweramp database.
There are two ways to resolve this, but I will give you easier one.
Use a tag editor (Auto Tagger) and search for the 'rolling stones', in the artist field, rename the rolling stones to rolling stones2, then scan your library, make sure there is no more rolling stones, all changed to rolling stones2.
After that, go back to the tag editor and search for rolling stones2, and edit the rolling stones2 to how you want it to appear in your library, rescan library and you are done. Congratulations.
Bencherished