PackIcon Problem

[hxhgxy]

I hate to see so many errors in xaml, so I try to do some tests.

Case 1 (design mode): put PackIcon directly on window - no problem. put togglebutton on window - no problem. put popupbox on window - no problem

Case 2 (design mode) put ColorZone on window - all PackIcon disappeared except for the one inside of colorzone.

Case 3 (design mode) put more colorzone onto window - only the first packicon inside colorzone is still there.

This may be a problem with MarkupExtension, but I don't know what to do.
It would be great if the issue could be fixed in MD.

[hxhgxy]

I use textblock to replace packicon in togglebutton, the problem is still there.
So, the problem is with OnContent of ToggleButtonAssist.