Operating system: Windows 7
Graphics card: Geforce GTX 1060
Broken: 2.80, hash: 96f762500ef9, 2019-01-07
**Short description of error**
Vertices that are very, very close to each other that they are on top of one another can't be welded together using weld/remove doubles UV in the weld/align menu.
**Exact steps for others to reproduce the error**
Based on the default startup or an attached .blend file (as simple as possible).
1) Make a simple UV map for a simple shape like a box, and go to the UV map editor window to edit your UV map.
2) Split one vertex into two vertices so they are right ontop of each other.
3) Select both using any selection tool that works for you.
4) Open up the weld/align menu.
5) Choose weld or remove doubles UV to try and merge them together.
5) Deselect and select the "vertex" again and then move it around to see it still being split.
One workaround I found to this bug is to slightly move one vertex away from the other vertex, then select both and weld them again. Then it works.