Robocopy problems - skipping files and ignoring /IS switch

I'm experiencing a weird problem that I caot fix. I've simplified and narrowed down the problem in the following example:

I've got 2 identical folders:

D:test

D:dropboxtest

They both contain two identical folders, both with one identical picture (pic1.jpg).

testsourcepic1.jpg
testdestpic1.jpg

Now I'm using the following simple command: (twice for both folders)

robocopy "D:testSOURCE" "D:testDEST" "pic1.jpg" /IS /MOV
robocopy "D:DropboxtestSOURCE" "D:DropboxtestDEST" "pic1.jpg" /IS /MOV 

As expected, in the D:test folder, it overwrites pic1.jpg in DEST and removes pic1.jpg from SOURCE. (as per the switches)

However (problem) for some unexplainable reason, in the identical dropbox folder, it skips the pic1.jpg.

When I use /V on the command, I can see in the log that for D:test folder it sees the file as SAME, and overwrites as should using the /IS switch....

...BUT, in the dropbox folder, it sees the file as MODIFIED. The weird thing is they are identical. I can re-copy the pic1.jpg across all folders and nothing changes, it only skips the one in dropbox. /IT doesn't help either.

Even if it were modified, why is it skipping? Normally robocopy overwrites modified by default!! If I ACTUALLY modify the picture, it DOES work.

It makes no sense.

Any idea? Thanks