Depending on your local operating system, it’s very possible that Git didn’t recognize the change to the file because it was only a case change to the file name. A workaround may be to rename the file to something that will change the characters used in the file name, commit, then change it back.

for example:
Plan_m.php → Plan_m-temp.php → plan_m.php

You were almost onto the answer there. Renaming them, committing them and then renaming them back doesn't work, presumably because Git still has the file names with the incorrect case in its structure and just assumes it's the same file and merges them.

I've had to rename all of my models to something different and stick with it, which is incredibly annoying since it was a just a simple case mismatch. Seems very dumb to me.

Thanks for your help.

Maybe after doing the temporary rename, you can remove the old file from Git with something like:

$ git rm —cached Plan_m.php

That way it won’t have the old file to merge the new one with.