iTunes song tags revert back after editing

iTunes (Version 12.9.5.5) on my iMac (Mojave 10.14.5).

I imported MP3 files (not purchased files, I burned them years ago from CDs) by dragging them into iTunes. I open a couple songs (Song Info) to edit the album name. I change the word "The" to "the" (I want lower case, not upper). I also change the Comments, adding who played piano.

I close the songs and all is well. My edits are intact. But I open them again (Song Info) and the tags I just edited change back immediately, reverting back to capitalized "The" and the Comments I added revert back to blank (their initial value). I haven't done anything else - just opened the Song Info to view a 2nd time, and the change is immediately shown on both the newly opened Song Info window, and in the grid view of iTunes.

I checked file permissions, and I can read & write all MP3 files involve. I ran Disk Util on my external hard drive where the files reside (just in case something was wonky). I shut down and powered back up. It is repeatable. All 108 newly imported MP3 files behave this way. [Just yesterday I imported 18 songs from a physical CD and editing them works fine without magical reverting. Hmm.]