"invalid context" error messages

For several weeks I have noticed a strange error message when I run Forge. I see this message in the console when forge is run from within Eclipse. I also see this same message when I launch the forge jar file from my Mac's terminal app.
The four lines below all start with the string:
The four lines below all start with the string:
Date + time + my local network name
java[274] <Error>: CGContextGetCTM: invalid context 0x0
java[274] <Error>: CGContextSetBaseCTM: invalid context 0x0
java[274] <Error>: CGContextGetCTM: invalid context 0x0
java[274] <Error>: CGContextSetBaseCTM: invalid context 0x0