I'm wondering what service release you have. This clearly sounds like a bug, and one that may have been fixed.

Also, are you using the opengl preview? If so, are your OpenGL drivers up to date? Have you tried using the software preview mode? (Display, Preview Drawing, SreeD Software)

SR2.1 mentions many preview rendering problems:

Preview Render Engine

• Fixed case where applying certain materials would corrupt transparency preview (OpenGL Hardware shading only).
• Fixed case where applying certain materials would corrupt preview (OpenGL Hardware shading only).
• Fixed problems with Enhance Multilayer Transparency (OpenGL Hardware shading only).
• Made Preview transparency Settings persistent.
• Now always drawing current/active selected item with red outline in the Preview window.

---

Renderosity forum reply notifications are wonky. If I read a follow-up in a thread, but I don't myself reply, then notifications no longer happen AT ALL on that thread. So if I seem to be ignoring a question, that's why. (Updated September 23, 2019)