Scrambled image when setting Oppacity < 1 in an stl image

Support
1

Operating system: Windows
Slicer version: 5.12.0 and 5.13.0-2026-06-30 r34833 / d401fce

Expected behavior: Display .stl surfaces when setting “Edit Properties”: Opacity < 1.0
Actual behavior:

Slicer fills the screen with a scrambled unrecognizable image. The behavior occurs with MRI-derived files I have tried, but even also with a simple example stl file like the cube in

Thanks in advance for your help

Octavio