Power switch on AKG WMS40 wireless system

[itm]

I have an AKG WMS40 wireless system, and have an issue with the power switch on the (PT40) transmitter. The switch has 3 positions:
1.Off
2. Mute
3. On

My issue is that when I move the switch directly from position 3 (on) to position 1 (off), the unit often does not power off. If this happens I need to move the switch back to position 2, then to position 1 again, and check that the green LED has turned off. If I carefully move the switch from position 3 to position 2, then to position 1, it usually powers off as required.

The problem is that I often switch it directly from position 3 to 1, and don't notice that it hasn't powered off. Hence the next time I try to turn it on I find that the battery is flat.

Does anyone know if this is "normal" for this device?