Fixes #3106: Combo Box selection fixes

[MaciekWin3]

Fixes #3106 - The bug occurred because we were searching for an item in the entire collection instead of the filtered set. Additionally, I introduced a feature that deselects the previously selected item when the search text is shorter than the previous one. This ensures proper cleanup after the previous search.

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[fergusonr]

@MaciekWin3 Thankyou!