Good question and something I was not happy just leaving alone.
Once I satisfied myself that this was most likely not a bug but file corruption the questions that came to mind were...
(1) How this file became corrupted? and
(2) How extensive is the damage (physical damage, system wide, file specific)?
As mentioned I currently use Linux so needed to find a method to check the file system for errors and see if any blocks or clusters were damaged. I am assuming here that I could of had a power spike or jolt to my machine that could of caused the platter on my hard disk becoming damaged.
I did this by running 'fsck.ext4' from a LiveCD on all my hard disks. It took all Saturday to do this. Thankfully no errors were detected. Anyone interested in how I did this can check out my more specific response on the Ubuntu Forums...
http://ubuntuforums.org/showthread.php?p=11152491#post11152491
This left me with an event that could have occurred while the affected file was open that could have resulted in the identified corruption. In fact, on reflection I did have a power blackout 3-weeks ago! I know pretty much exactly when it occurred and so was able to work out exactly what I was doing... as it turns out I was editing the exact sheet in the corrupted file that contained the corrupted image!
As LO had 'recovered' the file; all text, formula and images were present and encountered for; and rendering as expected, I never even thought the file was damaged; so much so that 2-weeks later when peculiar 'sheet/tab deletion errors' appeared I did not even connect the two events (power outage and corruption).
Thanks everyone for your help - I appreciate your efforts and suggestions.