It looks like you're new here. If you want to get involved, click one of these buttons!
If you double-click on a note from the home screen, you two copies of the note appear to be opened. If you left arrow on the one on the screen, it disappears and you are shown the second.
It wasn't happening on my main machine as it's timing related. but it turned out what's happening is you can click on a note in the list view whilst the transition animation opening the note is playing.
Thus, the double click was actually two clicks with the second one received during the animation.
This is fixed in the forthcoming 1.2.0 "calendar" release.