Music, memory leak?

Give this a try: boot into Safe Mode according to How to use safe mode on your Mac and test to see if the problem persists. Reboot normally and test again.

NOTE: Safe Mode boot can take up to 3 - 5 minutes as it's doing the following; 

• Verifies your startup disk and attempts to repair directory issues, if needed

• Loads only required kernel extensions (prevents 3rd party kernel/extensions from loading)

• Prevents Startup Items and Login Items from opening automatically

• Disables user-installed fonts 

• Deletes font caches, kernel cache, and other system cache files

This is the first reporting of a Music issue. By chance did you change the color of the cursor in the System/Accessibility/Pointer preference pane?

Doing so does cause a memory leak in Safari. If you have changed the color try setting it back to the default black and see if that helps.

If you close Music and reopen it how long does it take to build up that far?

This is the exactly same problem. When I maximize my mini player with it's lyrics on, it crashes.

which song were you listening to by the way? I think the problem occurs when I play certain songs.