I haven't seen "shorter than expected" message before, sounds like a Mac
OS X specific thing.

As for never getting any probes out, this is where it gets fun.
Debugging this is very tricky indeed: it involves you dropping into the
kernel debugger and looking at the interpreter's state. Most likely, the
compiler is doing something different with the relevant Python
functions, causing the logic in the DTrace ustack probe to fail.

I don't even know how the Apple guys debug this sort of thing, but
they'd definitely need to be involved.