Editor not letting users put spaces in?

All of a sudden we are getting complaints from people who are trying to post to their blog and when they hit save all of the paragraph spacing is gone. They say the only way they can get it to work is to go into HTML and put it in manually.

Has anyone had this happen - nothing has changed. No upgrade and no change to the style sheet.

A few come from MAC people but there are also complaints from PC users.

Any suggestions on why this would be happening. Is it on the users computer settings?

Thanks!
Helen