Operating system: Windows-10-10.0.17763 64 Bits
Graphics card: GeForce GTX 1080/PCIe/SSE2 NVIDIA Corporation 4.5.0 NVIDIA 430.86
Broken: version: 2.80 (sub 75), branch: master, commit date: 2019-07-29 14:47, hash: rBf6cb5f54494e
Short description of error
Even though auto merge is active, vertices laying directly on top of each other will not merge after create quad from vertex operation. auto grab is switched off in F2 settings. Increasing auto merge to higher thresholds (0.1) does not resolve issue and vertices won't merge when a quad is created from a single vertex selection. Does not occur with quad created from edge selection or more than one vertex selected.
Exact steps for others to reproduce the error
Turn off auto grab in F2 addon and leave other settings default.
Set auto merge to 0.001 or higher.
delete front face on default cube, grab any single vertex around the gap and fill it with f key.
The selected vertex (the furthest from the original selection) will not have merged with the one it now lays on top of.