Q: Only some photos sync

I've had an ongoing problem with photos on my photostream, in that only some of the photos I have on my iPhone sync to my Mac.  There doesn't seem to be any rhyme or reason to which ones get synced.  It's not the first or the last, it's just that random ones are missing.

Googling around, it looks like this is a very common problem.  Does anyone have a solution or a workaround?  It's very annoying.