@Troggie This is a mastodon issue unfortunately. Mastodon returns the most used version of a hashtag and they tend to not use camel case, unfortunately. However if you set CatsOfMastodon as a "featured hashtag”, you will get the proper case show up when composing since Featured hashtags get priority.
@ivory ah I figured there had to be a reason. Thanks for explaining. And thanks for the tip about the featured hashtag, I’ll make good use of that.