As noted in the description of the restriction, extrusions and rotation can also make vertices move off the grid. To ensure they all snap back onto it at the end you'll want to select the whole model and click/slightly move any vertex, once per top/front/side view.
3 years ago(+1)
It's easy to spot in the .txt file.
The cylinder went a bit lopsided (due to an extrusion I reckon because rotation is 0 on all axis as you can see):
She be a fickle beast, our picoCAD.
But by all means, the design and texturing is amazing. Love the ship. The boosters at the back have great detailing and the warp of the ground actually conveys speed - crazy!