New
#21
Well, I believe that I have found the cause of this problem. I run an auto-defragger utility (Iobit's Smart Defrag) that has a feature to auto-defrag my hard drives. For whatever reason, this utility was suddenly not completely releasing the drives via the Safely Remove Hardware applet... and as a result, was hanging onto the drive/drive letter in the background... this kept the drive letter(s) out of the pool of available drive letters when the drives were reconnected. Not sure why the system let me disconnect the drives in the first place... but when the drives were reconnected, the system saw that X: was assigned and just gave it the next sequential drive letter.
I have killed the Smart Defrag utility, and the system is again behaving as expected/wanted.
Thank you all for your help and suggestions.