To reproduce:
In a channel type ":D" then press Enter.

What should happen:
A message containing ":D" is sent to the channel.

What happens instead:
Emoji :registered: is inserted into the message.

In steps:

• After entering ":D", the emoji picker opens and is filtered to emojis containing the letter D
• After pressing Enter, the first emoji from the filtered list is picked, in this case ":registered:" and inserted into the message.

Slack solves this by not showing the emoji picker until ":" and two additional characters are entered. So ":D" would not show the picker, while ":DR" would.

I'm planning on adding options that control under what conditions the emoji completion popup will appear (and also the ability to disable it entirely.) Until then, as a workaround, simply press space or escape to dismiss the emoji completion popup. Ripcord will automatically remove trailing space from the end of messages when sending them.