Lowercase Letters Don't Serialize? フォローする
I've run into this issue, and it seems to go back at least as far as 9.2 (That's the oldest version I had readily avaliable to test).
If I take 2 serialized fields, using the default "Auto Alpha or Numeric" and make one field 'AAAA', and one 'aaaa', and print serialized labels, the capital letters serialize as expected (AAAB, AAAC, etc), but the lowercase letters stay put (aaaa, aaaa, etc.).
Yes, I can workaround this by using custom serialization or databases, but Basic users cannot.