Can't update email addresses in Membership 2 Pro. Certain characters "stick".

Hi. I'm using Membership 2 Pro and have been doing some cleanup to my members' entries. I've noticed on a few entries' email addresses, I can't edit them. If I try and update with a new entry, the old one sticks. Then I noticed that if I go in and change a few characters at a time, they'll usually change, but one character just refuses to go away. For example for an email address that WAS person@old-email.com that needs to updated to person@new-email.com I have this problem where I can't just replace the whole thing. If I try to go letter by letter (ie change a letter, then save, change the next letter, save...) it works up until a point. So like the "d" in "old-email" might stick so I can do something like update it slowly to person@newd-email.com.

I know it's confusing, but that's the best I could do to explain it.