HDD caddy causing Vostro 3750 to NOT power down?

Hi, I got a generic HDD caddy from eBay for installing a 2nd hard disk in the DVD drive bay. 

I ended up replacing the internal HDD with a SSD, did a clean install of Win7 on the SSD, installed required drivers, booted up and and checked that everything was fine.  Great.

I then installed the original internal HD in the HDD caddy from eBay, booted up and  checked that everything was fine.  SUPER Great! 

I was enjoying the much faster Vostro. Alas it was short lived. The laptop went to sleep mode (as configured) but would not awake from sleep. I had to hold down the power button to power it down and restart Win7. 

Had a look at Device Manager and found a couple of unknown devices. To cut a long story short, I compared the drivers I had in the original system with those in the clean install on the SSD and installed any missing drivers (there were 3 or 4 missing). Re-booted and checked Device Manager and no more unknown devices. However the problem remained. The system wouldn't wake from Sleep and while restarting I also found that the not powering down problem also affected Win7 shutdowns and restarts. Windows appeared to shut down normally (the screen would go blank) however the power button would remain lit. I left it for 1/2 to 1 hour to see if it would eventually power down. No luck, after a while the fan turned on continuously. The only way to power down was holding down the power key.

As a last test I removed the HDD caddy from the DVD bay completely and rebooted the system so it was only running on the internal SSD. Checked and the system now wakes from sleep and do normal shutdowns/restarts.

Not sure what else I could check at this stage. Would appreciate ideas from anyone who's had experience with HDD caddies. TIA.