Rice cooker not stopping? I bought a first rice/multicooker Tefal RK8121. I cooked the rice according to the manual.

I put the rice inside and added the steaming tray on top of the rice to steam at the same time (it doesn't say anything about that in the manual though). Added the water and started the program (with pre-washed rice). The program is one that automatically stops using some sensors inside the machine.

The rice is supposed to be cooking for 10 minutes, as written on the package. It didn't stop cooking, so after 40 minutes I had to stop it. The bottom of the rice was already a bit overcooked and the rice was mushy due to it being so long in there.

Why did it not stop? I tried it another time with wild rice, and it stopped itself after 30 minutes and the rice was perfect. But with white rice like Thai Jasmin, it didn't stop even after 40 minutes, this happened twice. I know somebody else who bought the same cooker and has the same problem, I guess there's something we must be doing wrong, but I'm not sure what.

The program used for cooking is rice/cereal.

What am I doing wrong? I tried both following the rice cooker's water advice, and the rice package's water advice and both without luck, the rice cooker keeps cooking the white rice for way too long.
Most ricer cookers use temperature of the pan - which is regulated by water content! - to decide when to stop. Only when enough water has evaporated to leave you with reasonably dry, palatable grains can the pan temperature exceed 100°C/212°F. If what you are cooking cannot absorb all the water, the device will cook until all the water has evaporated (which the lid makes very slow).

If actually boiling it dry doesn't stop it, and no "keep warm" or "saute" or similar special mode has been selected, return it, it is broken.