New ACT HP25E GPS weired behaviour

[Harald]

Today I got my 25E GPS out of the drawer and turned it on. Batteries wer flat, as I had left it there unused for a couple of month. Installed a battery pack with fresh batteries and switched it on again.
But what is this? Looks strange:
   

I can press a number key and the number gets displayed. I can't do any basic operations though and other keys do weired things. For example x<>y seems to divide by 100. R/S gets me to stopwatch mode, and that even works. None of the menue options work.

I haven't tried reflashing the firmware. I am sure the calculator worked fine last time I played with it.

Any thoughts on what might have happened here?

Cheers,
Harald

PS: Bernhard, I hope you don't mind me posting this here instead of emailing you. It is not meant as a complaint in any way. I just thought it might help others if they have a similar problem.
It might be me having made a mistake when installing it. Maybe an insulation has been pierced under pressure inside the calculator and now there is a short?