Member being moved spontaneously to Former Member tab

I realize this might not be a completely new topic but I haven't found a solution by searching precious similar posts.
One (just one so far) of our members keeps being spontaneously moved from the Members tab to the Former Members tab.  No one is moving her there.  She is an active, paid up member.  We have received a couple of messages saying she has been moved because she is no longer a member.  Usually she just appears there without any notification.  I just moved her back to the members tab a couple of days ago and when I logged in today I got the message that she was moved to former members and once again I just moved her back.  Any assistance to stop this happening would be appreciated. 
Thanks

Wild Oats 2849

Please disable the 'Add "Not a Member?" links' checkbox in your Email & Contact forms module (Email Security tab)
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Thanks.
I have done this.  I hope it works.  When it first happened I thought that perhaps she had accidently clicked that.  She said she didn't.  It even happened a few times when she was on vacation out of the country.