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Marker sync does not work correctly if moving strip so it overlaps another strip
Confirmed, NormalPublicBUG


System Information
Operating system: Linux-4.15.0-39-generic-x86_64-with-debian-buster-sid 64 Bits
Graphics card: GeForce GTX 780/PCIe/SSE2 NVIDIA Corporation 4.5.0 NVIDIA 390.77

Blender Version
Broken: version: 2.82 (sub 6), branch: master, commit date: 2020-01-09 19:46, hash: rB9d95c035c599

Short description of error
Moving (grabbing) a video strip with a marker through it, and Sync Markers enabled, fails to update the marker location correctly if you drop the strip on top of another strip.

Exact steps for others to reproduce the error

  • Make a new Blender Video Editing project
  • Add two videos (or image sequences) to the sequencer.
  • At the first frame of the second (right-hand) strip add a marker with M. In the example I named it "second video". (first screenshot)
  • Go to Marker menu -> Check Sync Markers option
  • Grab the second strip and move it around to confirm the marker moves with it. (second screenshot)
  • Now grab the second strip and drop on top of first strip (near the end). The border will turn red (third screenshot) and when you release the mouse the strip will snap to the end of the first strip (as expected).
  • However the marker moves to where you tried to release the mouse, not where the strip actually ended up. (fourth screenshot)
  • The marker is now permanently offset by the difference between where you released the mouse, and where the first strip ended.

Two strips with a marker at the start of the second strip:

Moved strip to the right, marker follows it:

Overlapped move in progress, strip is highlighted in red:

When mouse released, strip snaps to end of first strip, however marker stays where it would have been if it had not snapped:

It appears that the code to update the marker position runs before the check for the overlapping strips is made.