Converting wav files changes peak values
 

I just imported a 44.1kHz/16bit wav file into an empty Pro Tools session. Since I always work with 48/32, it converted the file to fit the session. However, when playing back the file, I got peak values of up to +1.1 db.
I've never seen this before. Is there anyone who can explain why this is happening? Is the experienced volume changed as well, or is it merely a digital circumstance that the peak value changes? Is there also a rule of thumb when to be careful with this?

Lots of question, I guess I'm just surprised :)