$&@“$ autohide taskbar. It often won’t come up or won’t hide when you need it to.
Of late, mine seems to be behaving itself (in current build of Win10). But it definitely used to be flakey like that. Wouldn't surprise me if it starts acting up again.
Several other recurrent problems with Win10 (like start button suddenly stopping working) seem to have gone away with successive updates. I almost don't mind it now even if I still don't care for the aesthetics of "Metro".