Unfortunately, we still haven't implemented the desired behaviour. Until recently, we haven't really spent much time debating on what the behaviour should be.
We did agree on behaviour similar (if not the same) to what you have suggested. Namely, if the control has width different than the default one and no dropdownwidth is specified, the dropdown should be as wide as the control.
There are few other scenarios we would like to clear out and then the item will be pending for implementation.
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