I would like to report a problem with SketchUp for web. The top surface of this tablet stand is rectangular but after rotating the vertical line the top surface is broken into triangles and extrusion is not possible…
There’s probably a reason. Share your .skp file.
It is a file in sketchup for web… SketchUp
I know that. You mentioned that in the title. Please share the .skp file so we can examine it. You only provided a viewer link. Download the file to your computer and upload it in a reply here.
Senza titolo.skp (128.4 KB)
Heh , Does it in the desktop version for me too.
The uploaded model already has a diagonal. If that is erased I have no problem rotating the edge.
If I click the rotate tool onto the line , the diagonal pings back after erasing it
Not sure what else I can say.
SketchUp : YMMV 
Prior to recording that it was creating the geometry and it was staying, as soon as I clicked the end point
I wonder if Length Snapping is once again the culprit. It is on on the model. If it made the Rotate tool grab a point that is ever so slightly off from the intersection of the edges, it might distort the face. But in even that case the extra splitting edge should appear at the intersection…
Not for me. I left ‘Length Snapping’ on and/but set units to mm end to highest visible precision. Top face endpoints (five) are all coplanar. Deleted the diagonal. Rotating the short edge (like in @Box’s gif) temporarily shows a new diagonal but that vanishes after rotating the edge, completing the operation. This sort of temporary hidden geometry is often visible during certain operations without creating them in the end.
