iPhoto unwanted Iconversion of images to thumbnail resolution

[PhiladelphiaJ]

Hi Everyone,

I found one picture in my iPhoto library that was unexpectedly blurry. I deleted it, only to find the preceding picture became blurry too. This happened again when I deleted that one.

Rebuilding the library corrected this but I'd like to prevent this happening again. Any ideas?

Thanks for your help,

J.