It turns out IE 8 has a so called "Compatibility Mode" that effectively emulates IE 7 behavior (bugs). One of the bugs with compatibility mode is the scrolling behavior of div.autoscroll, like in the issue list:
When a horizontal scroll bar appears (many columns selected), the horizontal scroll bar overlays the issue list, a vertical scroll bar appears and the height of the issue list is not expanded correctly. With only one issue in the list, this makes it impossible to read the details in the table. Firefox does it right in any version, Safari too, IE 8 can do it right if it's not in Compatibility mode. Unfortunately IE 8 defaults to compatibility mode for sites in an intranet (at least in our company). Asking all users to use Firefox or reconfigure IE is not a good solution.

There's a way to tell IE to disable compatibility mode with a meta tag:

This makes each IE version specified here use it's native behavior (ordering is important: newer ones need to be first). Firefox and Safari are unaffected by the change.

Patch against Redmine 1.2.3 attached. Applies cleanly to 1.3.0 and trunk as well.