iPhone crash / contact photos switch?

Hi

Anyone else having this problem - my iphone 4 has crashed twice in the last couple of days - well, it just malfunctioned so that all the apps crash when I try to open them, so I have to turn it off/on. When I turn back on, many of the photos on my contacts have swapped around.
I know it isn't a big problem but it is a bit annoying - just wonder if it has happened to anyone else?
I am running ios 5.1.1 - didn't upgrade to 6 because I didn't have the memory and heard that it was a pain in the a** - but could this be the problem?
Any thoughts appreciated

Thanks