Fcitx5 IME deactivates for the first character typed after sending a message

[Xenapte]

Describe the bug

When typing with an input method editor, pressing Enter to send a message causes the IME to turn off for the very first letter of the next message. The first character is input as raw ASCII, and the IME only activates starting with the second character, which makes typing extremely annoying if you're a CJK-language user.

Screenshot:

Notice that after sending the first message, the next key I pressed got typed in as raw ascii instead without triggering my IME.

Reproduction

1. Install the Fcitx5 IME and configure as needed
2. Go into any chat room, switch the IME on, type something and hit enter to send the message
3. Try typing again.
4. Observe that the first character you input escapes the IME and gets put directly into the text box.

Expected behavior

The IME should work as long as I don't switch it off myself.

Platform and versions

OS: Arch Linux (kernel version: 7.1.10)
Browser: Firefox (both the latest 154 version and 153 ESR)
Sable version: v1.21.0 (7675aa1)
Homeserver: I don't think that matters

Additional context

I can't recall if older Sable versions had the issue (given that I've been using it for ~2 months for now, probably no).