If set to ASK and adequate FROM and TO video remains on each side of the cut, to cover the dissolve length, a prompt wouldn't be expected. Varying transition lengths tested here do not overlap or shorten the video.
However, when the transition length is revised in the effects window - made longer or shorter, but still with adequate excess FROM/TO video - the prompt does appear. That behavior isn't bad, but seems somewhat inconsistent with what would be expected.