I encountered a rather annoying issue with post tags where added tags would not save either during initial publish or editing.
After searching for a while I didn't find anyone with the same problem as I was having but luckily I was able to figure out the issue and wanted to document it here in case anyone else runs into the same problem.
My "Posts" are products which I tag with a general price such as "<$10" among other tags. It's the less than sign that seems to cause the issue.
By adding a space between the "<" and the "$" the problem is fixed. I'm not sure if this is a bug, or intended behavior. A tag such as "<$10" causes no tags to save, but change the tag to "< $10" and everything works as expected.