2nd HD ultrabay adapter is not recognized in Advanced Dock

[basketb]

I recently found out that my Advanced Dock has the following problem:
The Ultrabay Enhanced port in my Advanced Dock works well when I put in my ultrabay slim CD/DVD-RW (can read/write DVDs, can eject the drive, reinsert it, etc. without problems). However, when I put the 2nd HD ultrabay adapter from the Thinkpad (T60p in this case) into the dock's ultrabay port, I cannot get the HD to show up in Windows explorer or the disk manager for that matter (yes, the HD is initialized, formatted and contains data). Sometimes it shows up in the "remove hardware" tool (as USB drive, which is expected, but without a drive letter, which I would not really expect). Sometimes the green light of the HD adapter comes on and stays on when the adapter is inserted into the dock. But nothing else happens. When I put back in the DVD drive, it works flawlessly. Same when I warm/hot dock the Thinkpad (DVD drive is recognized, HD adapter is not). When I cold boot the Thinkpad attached to the dock with the HD adapater in the ultrabay port, it takes ages for the Thinkpad before it actually boots up (from the internal HD). Without the HD adapter in the dock, the Thinkpad starts up normal.
The problem occurs with both the SATA and PATA HD ultrabay adapters. And both of these work without problems in the Thinkpad and in another Advanced Dock (so I don't think its either the adapters or the HDs that are the problem, and yes, these are genuine Lenovo/IBM adapters).
Thus, I assume there's something wrong with the (Ultrabay Enhanced port of the) Advanced Dock, but what? (given that the DVD writer works without problems)
Not sure whether the problem has always existed or not as I've never used the 2nd HD adapter in the dock before. I actually do not need to use it in there but it sure would be nice to know what the underlying problem is. Any suggestions?