Please help : Strange 'file has vanished' behaviour with rsync on windows.

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Please help : Strange 'file has vanished' behaviour with rsync on windows.
I need to run rsync on windows and sync shares thru UNC names.
When I try :
rsync -e ssh -av //mypc1/myshare1/dir1/* //mypc1/myshare1/dir2/.
rsync does a copy but says "file has vanished" for every file.
Then when I run: 
rsync -e ssh -av --dry-run //mypc1/myshare1/dir1/* //mypc1/myshare1/dir2/.
it shows me all the files-- indicating that all are out of sync.

I need to encode logic to transfer only when needed, and this is not helping.

On the other hand, just to test, if I did a copy without going to network,
rsync -e ssh -av /cygdrive/c/myshare1/dir1/* /cygdrive/c/myshare1/dir2/.
and then run:
rsync -e ssh -av --dry-run //mypc1/myshare1/dir1/* //mypc1/myshare1/dir2/.
it shows me no files --indicating that the dirs are in sync.

I would have to use UNCs to copy.
Is there a bug that I am encountering?
How do I make things work?

Best regards