i'm giving a trick:place block the vector [789.1, 22.00, 1116]
and psi is placing a block at [789, 21, 1115]
/setblock command places a block at [789, 22, 1116] if given the coordinates [789.1, 22.00, 1116]

How to recreate: Set saved vector 3 to the vector of a known block in the world. put this spell into a normal spell bullet, stand near the block and activate the spell bullet. The coordinates of the block placed will be off by 1 on the y and z coordinates. (note: a block next to cad is required)

This actually relates to the other issue you opened. When psi shortens a axis of a vector, it rounds it off. So it can sometimes look like psi isn't lining up vectors correctly. Im guessing that the z axis of that vector is between 1115.5 and 1116. so when it gets shortened to a max of 5 displayed characters per axis, it gets rounded up and displayed as 1116.

Works as intended