Tiny issue/annoyance but I've noticed this slows down my tagging process at times and I don't see why it shouldn't behave this way instead.
Basically, the stored tag value is "Uncompromising" so I type in "un" and Musicbee autocompletes to "uncompromising". Pressing Enter here results in the tag value being saved in lower case, even though there was no such value stored in the beginning, giving me duplicate values with different capitalization.
That behavior would make sense if there were values stored consisting of both capitalizations, but if there's not, I propose that this be changed so that autocomplete uses the capitalization of the stored value regardless of what you type in.
My example here is of the Mood tag but this behavior seems consistent across other fields such as Genre, Original Artist and so on: