Of a time to here, I can not need after some firmware update, I'm also having the same problem.
Users have passwords for accessing the NAS directories, but only when I access them through windows explorer do I have direct access to the NAS files without asking for a password.
Through any other type of device, android or linux, it asks for password normally.
I already cleaned the windows network mapping cache and there was no change.
My NAS is in firmware version v1.09 b06
Using Win7 - Direct access
Using Linux Mint - Request password
Using Android - Request password