[racket] Curious error messages

I'm currently using Racket 6.1. For some time now, when editing Scribble 
files in DrRacket, I've been getting "file has changed on disk" messages 
when trying to save or render - not consistently, just every so often. 
These are files I am not editing in anything other than DrRacket. I 
click "ignore" and everything works fine, but it is annoying.

Just now, when rendering a Scribble document, I see in the Interactions 
window the error "libpng warning: iCCP: Not recognizing known sRGB 
profile that has been edited". The rendering proceeds just fine. This is 
rendering to PDF using some included images that have been created using 
OmniGraffle. The same images used in render to HTML do not give such 
warnings. --PR