If you follow my other link you can see other videos and this is one of them,
Lady Lux Grohe Replacement Parts Plus - Bing video
You can pull this whole faucet and examine the A ring (between the faucet body and sink top) and even reconnect the water lines (and handle with cartridge) while you have it out, and inspect the hot water tube where it connects to the cartridge seat.
When you removed the cartridge what did you see in the valve body where the seats would be?
I follow HK's logic, and this would be an out of the ordinary situation, but something you can ask Grohe about.
As you see I like videos for general instruction and insights. Watch a few.

