Show sidebar doesn't work with IE11

With IE11, the "Show or hide sidebar" control will hide the sidebar when clicked, but will not restore it when clicked again. This apparently only happens with some spaces.

Steps to reproduce:
1. Go to https://confluence.atlassian.com/display/JIRAPortfolio/JIRA+Portfolio+Home
2. Click "Show or hide sidebar" or type "[" (Sidebar disappears)
3. Click "Show or hide sidebar" or type "[" (IE11: Nothing happens, Chrome: Sidebar reappears)

The only way I could figure out how to get the sidebar back was to go to https://confluence.atlassian.com/display/ALLDOC/Atlassian+Documentation
where I was able to restore the sidebar with the above control. I have no idea why "Show or hide sidebar" works in this Space but doesn't work on in the JIRA Portfolio space.