Slic3r support issues - not supporting big overhangs

I'm having trouble with Slic3r support structure generation. I'm trying to print a T-Rex model downloaded from thingiverse, and no overhang threshold setting produces support for the obviously-needing-support tail. Here's a screenshot:


Both overhang threshold settings of 30º and 60º produce output that looks like that image. If set to 90º, Slic3r just hangs (for hours at least, before i kill it).

A probably-unrelated bug is that any percentage setting of "Advanced > Support Material" causes Slic3r to produce support material that is mostly made up of a few sparse vertical lines. These are unlikely to support anything, see this image for an example at 80%. That does not look like the previous screenshot's support, extruded at 80%:


Thanks for any help or information.

-Zach

I've added this information to an active bug:
[github.com]