Post Comment button works intermittently in IE8

When attempting to add a comment to a review using IE8, the Post button frequently does not respond. Mousing over it, it does not highlight, and clicking it does nothing. Double-clicking it highlights the paragraph.

With some care, the user can hover over parts of the button until it highlights, at which point clicking it will work, but the clickable locations are inconsistent.

Repro steps:
1) Start at https://atlaseye-qa.atlassian.com/atlaseye/cru/CR-BAM-687
2) Click on "pom.xml"
3) Click "reply" on a comment.
4) Move the mouse over the "Post" button.

Observe that there are large areas of the button that can be moused over without the button turning blue.