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.
@shuttersparks you can file an issue in the official issue tracker starting here: https://github.com/mastodon/mastodon/issues/new/choose
FWIW instance admins are able to improve this by manually re-casing the hashtags in their admin interface, but it's a long and tedious process and has to be repeated with new hashtags that pop up.
