Standard Size mode (the Std button on the item designer’s top
panel) lets you type per-frame width/height values directly instead of dragging on the canvas.
Pressing Set commits those values and rebuilds the affected frame’s geometry.

What changed

When the frame you resize contains a plain mullion dividing it into openings (not a
coupler, which splits a whole facet into separate frames), pressing Set now
re-centers/equalizes the mullion so the resulting openings come out equal, instead of
moving the mullion proportionally from wherever it sat in the old layout. With a single mullion
this means it lands dead-center; with more than one mullion in the frame, they are spaced so
every opening (and its glass) comes out equal.