Homematic: Repeated PRESS_SHORT events?

I’m having a hard time trying to implement a toggle switch with a homematic push button (HM-PB-2-WM55-2) via homegear


Switch fernbedienung1  "Testbutton"  (Fernbedienung)   {homematic="address=MEQ*******, channel=1, parameter=PRESS_SHORT"}  

Switch testSwitch "Test Switch" (Fernbedienung) {exec=">[*:bash /etc/openhab/configurations/test.sh]"}

rule "Fernbedienung 1"
        Item fernbedienung1 received update
        if(testSwitch.state == OFF)
            sendCommand(testSwitch, 'ON')
        else if (testSwitch.state == ON)
            sendCommand(testSwitch, 'OFF')

When I press the button, the switch toggles as expected. But after a second or so, it toggles again. Does anyone have an idea what’s going wrong here? It looks like the button sends a retransmission of the PRESS_SHORT event, which is then evaluated again. But it just has to be an error on OSI layer 8, because this is such a basic use-case, I can’t imagine that this doesn’t work if done right.

Thanks in advance for your help!