Cannot open sidebar with shortcut or link when using Documentation theme with IE9

Steps to reproduce:

1. Go to a page with IE9 in a space that is using Documentation theme
2. Press '[' or click "Show or hide sidebar" button to hide the sidebar

Expected behaviour:
Pressing '[' or clicking "Show or hide sidebar" button should show the sidebar.

Actual behaviour:
Nothing happens.

Workaround:
Drag the sidebar open manually from the left side of the screen.