Labs: formatting sometimes switches itself off

### Steps to reproduce

1. Enable the WYSIWYG composer in Labs
2. Italicise, add a word
3. When at the end of that word, add underlining
4. Press space

### Outcome

#### What did you expect?
Word is italicised, space is underlined and italicised

`_word~~ ~~_`

#### What happened instead?
Space is italicised, underlining disables itself

### Your phone model

_No response_

### Operating system version

_No response_

### Application version and app store

Beta track, playstore

### Homeserver

_No response_

### Will you send logs?

No

### Are you willing to provide a PR?

No