Operating system: Linux-4.4.0-151-generic-x86_64-with-debian-stretch-sid 64 Bits
Graphics card: GeForce GTX 1080/PCIe/SSE2 NVIDIA Corporation 4.5.0 NVIDIA 430.26
Broken: version: 2.81 (sub 1), branch: master, commit date: 2019-08-04 08:21, hash: rBdd3cdf6f1e9d
Short description of error
When you have a 3d camera solution the active camera in the 3d viewport will display the positions of the 3d tracks as an overlay. When the camera is active you can select those tracks by clicking on them. The selection is synced to the tracks in the clip editor.
However, due to T68218 the selection often fails, and when it does Blender is changing the selected marker in a weird way.
Exact steps for others to reproduce the error
Open this file:
Nevermind the missing footage, the bug can be reproduced with a pink background as well :)
Select random tracking markers in the clip editor. You can see the corresponding 3d markers being highlighted in the 3d viewport as well.
With the camera still selected, click on the 3d markers (which look like empties) in the 3d viewport. The markers in clip editor are being selected as well, so everything is fine.
Now let's make it fail.
Click in an empty area inside the camera view, or try to select the cubes by clicking on their outlines.
In both cases the selection should fail, due to T68218.
However, notice how the selected marker is suddenly the one in the lower center of the frame.
To verify, select another marker in clip editor, for example the one on the right. Then in 3d view, with the camera still being the active object, click in the empty area in the upper right corner of the frame. Marker selection will jump back to the Track.016, in the lower center of the frame.
This happens with any footage I am tracking. There is always one track that the failing selection in 3d viewport will fall back to.