Can't confirm or deny myth status - I do, however, know that the PA28 of which I was (in fact, still am!!) a share owner went away for annual with serviceable vaccuum pump a few years back. 2 wks later, we were advised that the pump had to be changed as it wasn't working. The senior group member (who was a CFI of around 40 yrs standing) ran around muttering under his breath about 'mechanics turning the damn prop backwards'
I have since then been extremely cautious about turning the prop the correct way, but have never seen technical arguments for or against.