Changing ItemsSource selects the first item

[tmijail]

Current behaviour:

Since the 1.5 update, whenever ItemsSource is changed, SelectedItem is set to the first item in ItemsSource. This overwrites any selection that the user might have previously made.

AutoCompleteComboBox.bug.mp4

Expected behaviour:

If SelectedItem exists in the new ItemsSource, it shouldn't change. If it doesn't, the selection should be cleared.

Steps to reproduce:

See the demo in this branch. Specifically, this commit.

[vain0x]

Thank you! Released in v1.6.0.