Photostream deleted photos reappering

[ajo]

I have been trying to make sense of photostream, so have just taken some test photos, checked in iPhoto and they are there, which is great.

Now I tried turning off photostream on my iPhone, which said will delete all photos from my iPhone photostream, I ok'ed that checked back on my iMac later on and they where still there... also working great.

I have now just turned back on photostream on my iPhone and the deleted photos are back there (they are not on my camera roll as I deleted them from there to test this). I took a photo waited a little while and then turned off photostream on my iPhone to delete the recently taken photo, went back to my iMac and its there. I am guessing that they will have to be deleted from all devices or they will redownload each time as they are saved in the cloud?

I think like others I'm not quite getting how exactly photostream wants to work..

Are the photos still saved to my camera roll anyway or after the 30 days (1000 photos) will they start going from there, or do I have to manually save them to my camera roll...

Sorry if these are questions being repeated.