What a conincidence, that this just popped up. I've been having the same problem with the PC returning from sleep mode and wasn't sure if I don't have yet another broken Pioneer on my hands.
In windows 7 on PC wakeup from sleep the drive starts clicking as if seeking or checking for a disk for about a minute, and then stops responding to windows. This causes a couple of problems. Browsing to "my computer" causes explorer to lock up. I'm guessing its waiting for a response from the drive and just sits there. It causes the safely remove hardware tray icon to stop responding. In AHCI mode it lists all SATA devices + USB etc. The device driver dialog doesn't pop up in device manager for a couple of minutes after trying to open the device properties. After some time (10 mins, 15 mins, not sure) windows will just "drop" the device and windows will work fine with the device missing, until reboot when it shows up again, except that windows will hang when trying to shutdown so a forced poweroff is needed.
I had to disable the device in device manager, but if its a firmware problem, that's good news. Its good to know I'm not the only one with this problem. Sorry, not sure which firmware I'm running, I can't update it from windows 7 for some reason. P45 chipset, ICH10R controler.