Rob Klein wrote:
-------------------------------
"Suggestion 1:
Place a decoupling capacitor (100 nF) over the receiver."

If you mean by "over" between Vcc and Gnd, there is already a 100nF capacitor. I didn't draw it in the circuit. It is connected between the output of the 7805 and Gnd.


Rob Klein wrote:
-------------------------------
"Suggestion 2:
Could it be that the receiver reacts to fluctuations in light, caused by your hand moving near it?"

Definitely not. The receiver is in a black case pointing in the other direction (away from the buttons).