Pasting and editing multi line text removes line breaks

[ChristophWurst]

Describe the bug

Pasted multi line text shows with line breaks until one of the lines is edited.

To Reproduce
Steps to reproduce the behavior:

1. Create a new text file
2. Copy-paste

Lorem
Ipsum

4. Add a x after Lorem

Expected behavior

Loremx
Ipsum

Actual behavior

Loremx Ipsum

Screenshots
If applicable, add screenshots to help explain your problem.

Server details:

• Nextcloud version: 27.1
• PHP Version: [e.g. 8.2]
• Database: [e.g. MariaDB 10.6]

Client details:

• OS: [e.g. Windows/macOS/Ubuntu]
• Browser: [e.g. Firefox, Chrome]
• Browser version: [e.g. 22]
• Device: [e.g. iPhone6, desktop]

Logs

Nextcloud log (data/nextcloud.log)

Insert your Nextcloud log here

Browser log

Insert your browser log here, this could for example include:

a) The javascript console log
b) The network log
c) ...

[XueSheng-GIT]

The same happens if you create a markdown file locally with regular (single) line breaks and upload this file to nextcloud. Line breaks of the whole text are removed if you start editing in nextcloud. I assume this is the same issue.
Maybe related: #3568

[mejo-]

@ChristophWurst what you describe is already reported here, no? #4602

[ChristophWurst]

It sounds very similar but there are no unexpected linebreaks for me. I do expect the lines to break once and they do. If I modify the text there are no line breaks left at all