First key press not registered when on a call

[lleo_]

The W52P handsets behave as expected when you pick one up from a charging station or laying on a table with timed-out screen and start entering numbers. The screen wakes up and all keys pressed are registered and the number correctly displayed on the screen. All is good!

However, if on a call, and the screen timed out, i.e. went blank, the first key pressed is 'eaten', i.e. not registered only the screen is awaken. With the screen active you can press a key again and than is correctly registered.
This is not what is expected, especially for dedicated buttons like speaker phone or mute.

To be clear, on an active call, with the screen blank, timed out, one needs to press the mute button twice, but if the screen is active every key press is registered. I find this annoying and I am sure my customers too.
The only key that does not behave like this is on-hook/power. If on an active call, pressing on-hook/power will hang-up the call as expected, regardless if the screen is active or timed-out/blank.