Pressing ENTER key gives space instead of newline

I don’t know which community plugin is doing this (tried to check one by one, but couldn’t find out). This problem stops in restricted mode. Second time pressing ENTER key goes to newline.

Here’s my suggestion:
Disable half of your plugins and see if the problem persists. If it’s gone, then the issue is in the half you turned off. If the problem is still there, then it lies on the half that’s turned on.

Do this several time and you should home in on the problem plugin (or plugins)