Whether it's a persistent Taskbar, one that won't show up in front of certain windows, or just won't work at all in some cases, there's a reason. Apparently, a Taskbar bug (or "feature" as some might amusingly say) was introduced in one of the Updates released by Microsoft during August's Patch Tuesday.
If you're experiencing any of these issues, Brandon LeBlanc, Senior Marketing Communications Manager at Microsoft and the chief Windows blogger, has a solution for you. Posted to Twitter, Brandon provides a simple fix.
P.S. The fix is really more about toggling the feature. If find the option already turned on when you find it, turn it off and back on.