Comment 2 for bug 318285

It seems the issue is not yet fixed as the AcceptChildItem function for ThirdController is using the SupportsItem as "filter" but the item selected on the third pane is always a modifier item so the actual function call should be SupportsModifierItemforItems from the Act.

Currently Do not only still allows the wrong type of modifier item being selected but also in some cases filters the valid modifier item out.

I've pushed a branch trying to fix the issue here: lp:~d6g/do/3rd-controller-filter