Hi,
Isn't that because it was already translated before ? I tried on my end but I cannot reproduce that.
If you empty the translation, the translation is not emptied. That's because we want to avoid the case where an inexperienced user open the popup, click on save and then wonders why the name and description is not displayed anymore on the frontend even do he didn't change anything.
So when you have an empty field, it discard the change. If you want to remove a translation, simply unpublish it with the publish/unpublish icons next to the field, or unpublish/delete it via the Falang interface.
If you really want to "empty" the translation so that nothing displays for a translation, you can write in it and that will display an invisible space on the frontend.