Add relation form doesn't show up, when popup mode is selected

In-Portal has 3 window modes:

• modal windows
• popup windows
• no popups
  Also there is a relation feature, that allows to selected related category items/sections to each category item/section.

For example:
1. go to "Structure & Data -> Catalog -> Edit Link"
2. go to "Relations" tab
3. click "Add" toolbar button -> item selector will open
4. select an item and click "Select" button
5. relation properties window will open
6. change what's needed and hit "Save" toolbar buttn

What described is how it should work in modal and popup window modes.

However 5h item won't open, when popup mode is used in Internet Explorer 8+.