Not sure if a duplicate, but I have no idea how to check (the wording of other related issues may be completely different, so it's hard to find).
Kappa.pngKappa.png is sent and displayed as a text.

Kappa.png.png suffix.

I guess it should be more or less compliant with the webchat behavior.
So this came up again today, finding great amounts of abuse, because apparently highlights are parsed before this parsing corner case occurs (the .png being removed). Messages like Kappa.fourtf Would show up as just the emote in chat (no .fourtf suffix), but would highlight the message for fourtf.
Was fixed in a committi https://github.com/Chatterino/chatterino2/commit/84b1efcd242565283c03d8f67f11983f4fb5f1e6
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Was fixed in a committi https://github.com/Chatterino/chatterino2/commit/84b1efcd242565283c03d8f67f11983f4fb5f1e6