The Help Article on Drape indicates that you need to select edges to drape, not groups or components. Based on that information, I would be inclined to think that draping the edges from inside groups or components is the bug.
When you use the Drape tool, SketchUp transfers edges from a flat face onto a TIN’s curved surface.
Tip: To create the edges that you want to transfer onto your TIN, draw a rectangular face above your TIN. Then, draw the edges on the flat rectangle with the faces in X-Ray mode, so that you can see the TIN underneath. You can then erase the edges and faces you don’t need, leaving only the ones that you want to drape onto your TIN, as shown on the left in the figure (Callout 1).
When you’re ready to drape the edges, follow these steps:
- Select the edges you want to drape over the TIN.
- Select the Drape tool () from the Sandbox toolbar or select Tools > Sandbox > Drape .
- Click the TIN to drape the selected edges onto the TIN, as shown on the right in the following figure (Callout 2).
At this stage for you, unless you’re planning to upgrade to SketchUp Pro, it’s kind of a moot point, anyway.