[Feel free to change this to "feature request" instead]
Discussion at:
http://forums.cockos.com/showthread.php?t=120185
When rendering to stems, freezing, or gluing, if the disk is nearly full Reaper will not warn about low disk space (regardless of system pref) or explain that rendering failed due to running out of disk space.
Update: this seems to be true for the general render dialog as well.
Resultant items will be partial-length if the disk fills while rendering, or zero-length if the disk is already full, resulting in a very-hard-to-see item.
I think a warning that the disk filled while rendering is well in order. The big risk is that after using one of these routes to render to new files, the originals may be deleted if the user doesn't realize that the render failed.
Gluing:
Same thing with rendering a time selection: