Ultrabay HDD in X60t dock - weird behaviour

[zern]

I am experiencing this weird behaviour with an Ultrabay HDD in the X60t dock. Windows XP.

Dock the laptop – either when hibernated, or when running (hot dock).
Insert Ultrabay HDD, or Ultrabay HDD is already in the bay.
Windows becomes extremely sluggish, for a long time (multiple minutes) before the drive is mounted.
Transfer speed is about 1.5MB/s (megabyte per second). Measured with CrystalDiskMark.
Paltry. Unusable. Is this like floppy disk speed or what?!!

Boot with laptop in the dock, and Ultrabay HDD in the dock.
Window “freezes” halfway through the boot. The Ultrabay HDD lamp blinks regularly. Caught in some endless loop?
I have to eject the Ultrabay HDD so Windows can continue to boot.

After a fresh reboot (without the Ultrabay HDD in the dock), I then insert the HDD.
Windows “freezes”, extreme sluggishness, for a long time (multiple minutes) before the drive is mounted.
Transfer speed now jumps up to 33MB/s (megabyte per second).
Yay! That's about a 25x increase.

(Sometimes, Windows will go all sluggish when I open My Computer – the window remains blank. As if Windows is having trouble seeing the Ultrabay HDD it was writing to moments ago. Another symptom or a comorbidity?)

The same drive, in 3 different caddies: same behaviour.
The same drive, in the same 3 caddies, in a T60p: instant recognition by Windows XP. And always at the max transfer speed of 65MB/s. No sluggishness. (Yes, faster transfer rate on the T60p.)

Both systems and OSes are up to date. This issue on the x60t aside, both systems behave flawlessly.

Any ideas?
Deo you think the dock itself is faulty?

Thanks everyone!