When an item is selected in Microsoft Combo control, any manual change of text (including, but not limited to, deleting of entire text) will cause ListIndex property to be reset to -1. This is expected behavior.

Doing same in UniCombo will not case ListIndex to be reset after first keypress. That means, I can select all text and hit delete, emptying the UniCombo window, but the ListIndex will still be set to the row that was previously selected. This is incorrect behavior.
Only changing UniCombo text again will reset ListIndex to -1. As result, I always have to hit delete and then, for example, space button, to make code in Change event run as expected. In my case, having user press button twice is not acceptable.

Please please fix this bug, this would really take me a lot of time to rewrite all handlers of Change events.

Apologies that this does not work exactly the same way as the MS controls. As we've stated before we had to rewrite the MS controls from the ground up. We've tried to get everything to work in the same way, however there will always be some small behaviors that do not match up 100%. I hope that this does not invavlidate the use of the controls for you.