While developing a similar OLE container, I’m having the same problem as the Visio team had here. Luckily they have some weird fixes to the problem instead of explaining it so that other developers can fix the issue also. So currently I am trying to contact the Visio team for some more details.

The issue is with an MSWord OLE object with an enhanced metafile cache that simply dissapears when used with a COMPLEXREGION clipping region and a rotation transform (via SetWorldTransform).