Slideshow does not advance when beamer connected

[ubacher]

I wanted to use Imatch to show a slideshow on a beamer. When the beamer was plugged in the slideshow did not
advance. (Showed the first image).
(Fortunately I had a backup slideshow prepared!)

Today I tried connecting the laptop to my TV. Here all worked as it should.
I used a VGA connector.

Anyone else had tried this? I assume it must be a signal coming back from the beamer
indicating screen resolution or the like which makes the laptop output (i.e. change)  the screen resolution and which
in turn confuses IM. I can confirm that the beamer has a different screen resolution than the laptop while the TV does not.

Next time I have access to the beamer I will try starting IM AFTER plugging in the beamer and /or starting the slideshow
after I have plugged in the beamer.