There exists a bug in chat channels right now where two channels can be named the same, but have different capitalization. When this happens, the two channels exist independently, but a user cannot join each channel individually. If you're in the uppercase channel and you try to join the lowercase channel, you are booted from the uppercase channel.

Reproduction: Currently there are two reddit channels, named "reddit" and "Reddit". You'll find you can't join both at the same time.