Arpeggiator question/problem?

I just got my Slim Phatty yesterday, and I’m having lots of fun with it:-)
But today all of a sudden the latch function in the arpeggiator seems to act weird.
Whenever I have the arppegiator running and press the Enter/Store button to activate the latch funtion, it stops running the arppegiator pattern and just loops the last pressed key.
What could this be?
Have I maybe changed some settings by accident?