Support says I should submit the idea that it is important to sanatize input oder escape special characters.
After updating from 10.60 to 10.91 we figured that we had to re-enter the passwords for vmware and Hyper-V.
Support says hashing or something changed. Hashed passwords are stored in cell_info file.
Hyper-V Windows user login credentials contained a ">" character. After updating the password for a Hyper-V client, the cell_info file is wiped (ok, the other Hyper-V clients are there but everything else is gone).
Since > means redirecting of standard out it seems to me like a bug but support says the same rules for passwords apply to windows logins as for DP users. It worked before but that is no indication for a bug for the support.