In v1.5.6 entering a password in Admin (for an Admin or to reset for a customer) was encoding any "special characters" such as < or > or & symbols.

The fix can be applied manually by adding the lines shown in green here to the file mentioned:
https://github.com/zencart/zencart/c...14ecd658eb087f

Or just don't use < or > or & symbols in passwords! :)