Mine has a safety stop. You have to actually press a button to get it beyond that safe temp (I don't remember the actual value, but around 105-degrees?). Yours may only have that detent, and not have a physical hard stop. Part of the setup procedure is to adjust the temperature output. The idea is that for 'normal' people, you shouldn't need it hotter than the stop. They make you physically press a button to get it hotter on mine...sounds like yours makes you push beyond that detent.
If the thing was installed upside down, the plumber may have confused hot and cold. On many of the Grohe valves, you should only use the bottom output. If used for a shower only, to make it easier, he may have flipped the valve. Some brands I'm told can install the cartridge 180-degrees out of phase, which would compensate; I dont' think the Grohe valves can work like that. So, take the trim off, look at the valve, compare it to the drawings in the installation instructions or the picture on the website. It should be fairly obvious if it is installed upside down, or if the hot and cold are reversed.