Macro with body cannot be edited in IE

Steps to reproduce:
1. Create page and add a macro that has a body. For example the Excerpt macro.
NOTE: Do not type anything in the macro.
2. Click outside the macro and type something. Notice how the macro's body shrinks in size
3. Click on the macro body and try to type something.
Result: you cannot type into the macro body.

Reproducible on Win 7, IE 11 with Confluence v5.5.3 and v5.8.9