Do you have the latest version of Professional Editions installed? (4.7.936 or later?)
If yes, it may be caused by improved unpacking capabilities. The antivirus engine is in constant development, so when a new version is released, it's probably able to detect (slightly) more than the previous one, even with the same virus database. When the updated server version is released (probably at the end of the next week), the situation might reverse.
If you post the full path (i.e. including the possible packer tail) where Win32:Tibs-ADO [Trj] is detected in the Pro version, I might be able to verify.
