Hi,

We've located a problem that happens in XamComboEditor v11.2 (11.2.20112.1010) when a line exceeds width of XCE, but drop-down is already rendered. Below is a minimal setup for reproduction.

IE. click drop-down to make list stay open. When one _drags slowly_ the "car" down until "mmmmm" entries appear, application crashes in MeasureOverride. When one directly clicks on non-car area of scrollbar and list jumps directly to a place, no crash happens.

If one relocates the Id=20 entry to the top, so that it's immediately rendered into dropdown, it'll not crash here, but will when one scrolls to bottom (horizontal scrollbar disappears while scrolling).

Xaml:

<ig:XamComboEditor Name="XamCE" AutoComplete="True" CustomValueEnteredAction="Ignore" 
                           DisplayMemberPath="Code" Width="245" Height="22" />

Data:

public class A { public int Id { get; set; } public string Code { get; set; } }

XamCE.ItemsSource =
                new A[] {
                    new A { Id = 1, Code="aaaaaaaaaa aaaaaa aaaa"},
                    new A { Id = 2, Code="bbb bbb bbbbbbbbb"},
                    new A { Id = 3, Code="ccccc ccccc"},
                    new A { Id = 4, Code="dddddd ddd dddddd ddddddd dd"},
                    new A { Id = 5, Code="eee eeeeeeeee"},
                    new A { Id = 6, Code="f ffffffffff ff ff"},
                    new A { Id = 7, Code="gg gggggggggg ggg"},
                    new A { Id = 9, Code="h hhhh hhhhh"},
                    new A { Id = 11, Code="iiiiii iiiiiiiiii iiiiiiii"},
                    new A { Id = 12, Code="jjjjjj jjjjjj jjjjjjjjjjjjjjj jj"},
                    new A { Id = 16, Code="kkkkkkkkk kkkkkkkkkk"},
                    new A { Id = 17, Code="lllllllll llllllllllll"},
                    new A { Id = 20, Code="mmmmmmmmm mmmmmmmmmmmmm mmmmmmmmmm mmmm mm mm"},
                    new A { Id = 31, Code="nnnnnnnnn nnnn nnnn "},
                    new A { Id = 32, Code="ooooooooo oo oooo"},
                    new A { Id = 33, Code="pp pppp pp pppp"},
                    new A { Id = 35, Code="qqqqqqqqq qq qqqq"},
                    new A { Id = 38, Code="rrrrrrrrr rrrr "},
                    new A { Id = 40, Code="sssssssss ssssss"},
                    new A { Id = 50, Code="ttttttttt tttttttttttt tttt"},
                    new A { Id = 52, Code="uuuuuuuuu uuuu"},
                    new A { Id = 76, Code="xxxxxxxxx xxxxxxxxxx xxxx"},
                    new A { Id = 91, Code="yyyyyyyyy yyyyy"},
                    new A { Id = 98, Code="zzzzzzzzz zzzzzzzzzz"},
                    new A { Id = 101, Code="11111111 1111111111 1111111111111 1111111"},                
                };