Old question, but I just stumbled upon an answer that doesn’t require any extra code.
Enable autocompletion for the textbox and CTRL-Backspace should work as you want it to.
CTRL-Backspace deleting whole word to the left of the caret seems to be a ‘rogue feature‘ of the autocomplete handler. That’s why enabling autocomplete fixes this issue.
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You can enable the auto complete feature with setting the AutoCompleteMode and AutoCompleteSource to anything you like (for instance; Suggest and RecentlyUsedList)