SUMMARY
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STEPS TO REPRODUCE
1. import a video  on v1 with 2 audio tracks to autofill tracks a1 and a2
2. create audio track 3 a3, to target a new video audio track to it
3. target v2 and a3 on the timeline to import on those tracks
3. drag/import video #2 onto v2
4. get a warning/error on the bottom right saying: "audio split failed: no viable track"

OBSERVED RESULT
target tracks v2 and a3  were not filled with audio and video from video #2

EXPECTED RESULT
targeting a video and audio track should be the fallback of default import behavior for audio auto splitting/import.
targetting v2 and a3 the track importer should try to import onto v2 and a3  upon failed import on v2 a2 

SOFTWARE/OS VERSIONS
Windows: 
macOS: 
Linux/KDE Plasma: 
(available in About System)
KDE Plasma Version: 
KDE Frameworks Version: 
Qt Version: 

ADDITIONAL INFORMATION