ISPConfig 'forgets' user password
I'm running ISPConfig 2.2.27. One of my clients has a website/domain with two user accounts. For one of those accounts, ISPConfig seems to 'forget' the password every so often. The user can access her e-mail for weeks on end, until suddenly the password is no longer accepted. After I manually reset the password, the problem disappears and the user is able to access her e-mail once again for an indefinit period.
Is this a known problem? Can it be solved?