TYPO3 Core

If you insert an abbr or acronym tag typing additional text keeps the new text inside the new abbr or acronym tags.
IMHO it's quite hard and tricky to get out of the abbr or acronym tag and write inside a normal paragraph again.

A workaround I've used is to insert the abbreviations and acronyms after the entire text is written. Not the best solution from a usability standpoint.

This behaviour is different from, say, bold and italic tags, since you can disable them again by using the button (for abbr and acronym it's "insert" instead of "on/off"). And if you use the insert-abbr-popup to delete the abbr for only the selected text it deletes the tag completely.