Transferred photos to Mac via DiskAid, copied them to my synchronization folder on the Mac, then synced them back onto the iphone, where they are stored in the Photo Library album. When looking at them on the iPhone after the transfer, the photos originally taken in portrait orientation (phone held vertically) now display on the phone rotated 90 degrees. The photos originally taken in landscape orientation (phone held horizontally) display properly.
No email was involved, and no PC was used. Interestingly enough, the photos on the Mac are displayed either correctly OR rotated as on the iPhone, depending on what app I use to view them, so the earlier post that mentioned it being linked to viewers seems spot on. I have no clue as to why the photos would display properly when originally on the phone in the camera roll album, but display incorrectly after being transferred off the phone then back onto the phone into the Photo Library album. The iPhone should be using the same viewer regardless of what album the pics are in, I would think.