Edit: Thank you @Gorgious, scaling the points to the 2D cursor worked. I hope blender updates Constrain to image bounds to work properly with UDIM tiles.
I'm trying to set the y-coordinate of a bunch of vertices to 0. (Some of my vertices are less than 0 and it causes issues in external software.) I select the vertices, and set all their y-coordinates to 0. I should not have to worry about floating point inaccuracy since 0 has a perfect representation. Yet entering 0 as the y-coordinate does not set them all to 0, most are a bit above or below.
If I try to set them one by one, the first one gets set to 0 properly, but then setting the adjacent one to 0 messes up the previous one again. What on earth is going on? Attached a picture of my UV layout and the vertices I'm trying to set.