Purging histories also purges (permanently deletes) all of the datasets inside it.
There is likely some issues with the log out/in function with respect to resetting quota (or a related issue that results in the same behavior). Our developers are aware of reports of end users having problems around this. Seems to have started around the middle of last week. We have been unable to reproduce this with internal testing, but I’ll follow up with them again next week.
Meanwhile, if you or anyone else has a quota reset issue, contact us and we can reset quota from the admin side.