I have a similar problem (left panel won't stay open) but for me F10 doesn't do anything! The F11 works normally, but F10 is completely dead.
I work on a laptop, and when booting with out the docking station, my left panel is always collapsed no matter what I do. When booting connected to docking station, my left panel is open and stays open.
I don't enjoy rebooting just to get the Evernote left panel and F10 to work properly. Is there any way to fix my F10 with out a reboot?