I'm not sure where to report suggestions or problematic behaviors to the Mastodon development team.
This one is an intentional behavior, not a bug.
To help those who use screen readers, we are suggesting to newcomers that they use #CamelCase on hashtags so that screen readers read the text correctly. However, Mastodon's post compose window often changes camel case hashtags to all lower case. It seems to do this if the hashtag is a popular one.
It might be good to leave hashtags alone, as written by the user, instead of overriding with what Mastodon thinks the user meant to type.
@jrosen707 That would be okay. Sometimes I've typed in camel case and when I do a quick proof before hitting Toot I notice they've changed to lower case. Exactly how and when that happens I'm not sure.
What do now is recheck and fix the hashtags immediately before hitting Toot and they "stick".