Surely this is how it should be.
Defragging is invasive surgery,
like transposing two legs and hoping that afterwards the patient will still be able to run.
Swapping the arms over at the same time could be tricky.
CCleaner is NOT relocating an essential file or folder and expecting continuing functionality.
It is merely chopping out something that should not be present,
and if a second instance of cleaner is running the first one will hit the spot,
and the second one will probably just move on to hit the next spot.
Personally I would never run two instances of CCleaner simultaneously,
it could not possibly clean the system drive any faster.
I ALWAYS run a second instance of CCleaner to ANALYZE ONLY once the first instance has first ANALYZED,
But ONLY when I wish to compare the difference between two versions of CCleaner.
This allows me to compare two analyze screens side by side,
and see if the next version makes any difference on my specific system,
and then I investigate the consequences to my specific system.
I am able to do this by using the Portable versions of CC.
I do not know what could happen if two installed versions were using the the set of registry keys,
but it would be fun watching what it did - to some one else's computer ! ! !
Alan