It is a Dropbox folder. Just to be certain I repeated the test with a regular folder and indeed the behavior is different.
]It sill doesn’t pick up the hidden flag on renamed but does delete it when I remove the file.
I find this odd, because the Dropbox folder is (should) not (be) special. I have not converted to the new model of Dropbox which uses Cloud technology. Anyway, the main point being that the hidden flag is not picked during rename remains.