I am suffering from the same problem in Opera 24 with Windows 8.1. Whenever I press the windows-button, the start menu, but obviously not the taskbar pops up.

It doesnt happen all the time, but at random moments.

Is there any way to fix this without having to resize the screen all the time? This issue is preventing me from working efficiently.

You can disable the bookmarksbar by going to options and type bookmark in the searchbar. You'll get an option to enable it. Simply untick it and it's done.