When I type something, it may look like "Hello,how are you doing?" instead of "Hello, how are you doing?"
The comments section and posting system.
e621's posting system should implement proper spacing after punctuation.
Commas and periods are sometimes not spaced, meaning I have to edit posts and double space.
All the time.
No, I can't reproduce the bug every time. Often times, it's only in the comments and not forum posts.
Editing posts after I made them and double spacing. I still don't double space almost ever. It's extremely inconvinient.

Old issue, completely harmless. It rights itself when you refresh the page.

What BlueDingo says, old issue, refresh "fixes" it.