AutoDesk Smoke :: Lost Render File When Creating Subclip Or Dragging

I have a multi layer in my timeline , full graphic motion and long render. The base layer (layer 1) is a SOLID LAYER.

1. i select all that segment (multi layer) that has been rendered (yes, it's rendered). Now i drag it into my desktop (thumbnail view), but what happen is new clip is unrendered. So i have to re-render that clip. Why ?

2. i select all that layer, and collapse it ( contain selected). It collapse into a single clip but also i lost my render in my container. why ?

3. i mark in/out and create subclip. again i got the subclip but it's unrendered.

4. i mark in/out and drag into other timeline (same setting). and the pasted segment has no render file.