Not sure why you would expect only the video split to insert if no audio split is defined. These operations are intended for all selections on both video and audio, and If there is no audio split defined then all the audio is considered selected. Same with video. If you define seperate audio and video splits, then just these selections are inserted. The drag video/audio-only operations are there if that is what you want to do.
Correct for Clips opened from Sequence
The idea behind the expected common-sense behaviour is to avoid Mouse in some cases, to aid some keyboard driven workflow - to avoid activating Timeline to select/deselect Audio/Video Tracks when only Video or only Audio is needed to place in the Sequence when clips are opened from Project panel.
The Splitting feature is not ultimate, currently it can be used solely for doing J and/or L cuts.