Sometimes when I click a Notes icon, the Notes section opens and immediately closes (or closes and reopens) just as if I had double-clicked. Obviously I thought this was something to do with my mouse.
Then I noticed that this only happens with empty Notes. I have observed it for a while and it never seems to happen with those Notes that actually have something in them, only those that are completely empty.
The workaround seems to be to click on the corresponding icon of some other task that has text in its notes section. Although this doesn't really fix the problem, it seems to "calm it down" a bit, enough to be able to get some notes in :)
I was not able to reproduce this problem. Can you please let us know what web browser you are using, and if you are referring to the Notebook section or the Tasks section. Also, do you have your list displayed in the grid format or the multi-line format?