Issue 1:
I've reduced this down to about bare minimum:

use std;

native mod foo {
fn bar(x: int);
}

obj new(i: int) {
fn f() {
str::as_buf("", {|_x| foo::bar(i) });
}
}

Errors out with:

rust: upcall fail 'Assertion cx.fcx.llobjfields.contains_key(did.node) failed', ../src/comp/middle/trans.rs:2679
rust: domain main @0x102029600 root task failed

Issue 2:
The following code crashes rustc f05eaa4 (2011-12-09):

use std;

import std::option;
import std::ptr;
import std::str;
import std::vec;
#[link_name = "pcre"]
native mod _native {
type _pcre;
type _pcre_extra;
fn pcre_exec(re: *_pcre, extra: *_pcre_extra, subject: str::sbuf,
length: int, startoffset: int, options: int,
ovector: *int, ovecsize: int);
}

obj pcre(_re: *_native::_pcre) {
fn match(target: str) -> option::t<[str]> unsafe {
let oveclen = 30;
let ovec = vec::init_elt_mut::<int>(0, oveclen as uint);
let ovecp = vec::unsafe::to_ptr::<int>(ovec);
let r = str::as_buf(target, { |_target|
_native::pcre_exec(_re, ptr::null(),
_target, str::byte_len(target) as int,
0, 0, ovecp, oveclen)
});
ret option::none;
}
}

Stack:

(gdb) bt full

#0 upcall_fail (expr=0x5fd750 "Assertion cx.fcx.llobjfields.contains_key(did.node) failed",

file=0x5fd790 "src/comp/middle/trans.rs", line=2914) at ./src/rt/rust_upcall.cpp:65

No locals.

#1 0x0000000000445ef1 in middle::trans::trans_local_var::_adf4c1777aa541de ()

No symbol table info available.

#2 0x00000000004469ac in middle::trans::trans_var::_d1e14f52b7acf547 ()

No symbol table info available.

#3 0x00000000004461b0 in middle::trans::trans_path::_5717eb102c51bae9 ()

No symbol table info available.

#4 0x0000000000448af2 in middle::trans::trans_lval::_1f6f126aa370757e ()

No symbol table info available.

#5 0x0000000000450c41 in middle::trans::trans_temp_lval::_1f6f126aa370757e ()

No symbol table info available.

#6 0x000000000044ca53 in middle::trans::trans_arg_expr::_f2ab945cefa5f446 ()

No symbol table info available.

#7 0x000000000044dde0 in middle::trans::trans_args::_5b185ed913f17816 ()

No symbol table info available.

#8 0x000000000044e1ea in middle::trans::trans_call::_9bc861feeed3fbef ()

No symbol table info available.

#9 0x0000000000451be9 in middle::trans::trans_expr::_e7480723aeaebdfe ()

No symbol table info available.

#10 0x000000000045873b in middle::trans::trans_block_dps::_95df69d395a561cc ()

No symbol table info available.

#11 0x000000000045a884 in middle::trans::trans_closure::_5f30b7b117e0c7c7 ()

No symbol table info available.

#12 0x000000000043e92e in middle::trans::trans_expr_fn::_9276f38be3371c81 ()

No symbol table info available.

#13 0x0000000000451ace in middle::trans::trans_expr::_e7480723aeaebdfe ()

No symbol table info available.

#14 0x0000000000450b1c in middle::trans::trans_expr_save_in::_58e068603372c187 ()

No symbol table info available.

#15 0x0000000000451093 in middle::trans::trans_temp_lval::_1f6f126aa370757e ()

No symbol table info available.

#16 0x000000000044ca53 in middle::trans::trans_arg_expr::_f2ab945cefa5f446 ()

No symbol table info available.

#17 0x000000000044dde0 in middle::trans::trans_args::_5b185ed913f17816 ()

No symbol table info available.

#18 0x000000000044e1ea in middle::trans::trans_call::_9bc861feeed3fbef ()

No symbol table info available.

#19 0x0000000000451be9 in middle::trans::trans_expr::_e7480723aeaebdfe ()

No symbol table info available.

#20 0x0000000000450eea in middle::trans::trans_temp_lval::_1f6f126aa370757e ()

No symbol table info available.

#21 0x000000000045624b in middle::trans::init_local::_6fb0f262f37ff83d ()

No symbol table info available.

#22 0x0000000000456dc2 in middle::trans::trans_stmt::_c6405279a5bafb3f ()

No symbol table info available.

#23 0x00000000004584df in middle::trans::trans_block_dps::_95df69d395a561cc ()

No symbol table info available.

#24 0x000000000045a884 in middle::trans::trans_closure::_5f30b7b117e0c7c7 ()

No symbol table info available.

#25 0x000000000045ab8b in middle::trans::trans_fn::_3faad8b8f452ee78 ()

No symbol table info available.

#26 0x00000000004848a1 in middle::trans_objects::process_normal_mthd::_58e8157eea4a94d2 ()

No symbol table info available.

#27 0x0000000000480b2d in middle::trans_objects::create_vtbl::_2bedb929f9a5e9c4 ()

No symbol table info available.

#28 0x000000000047bceb in middle::trans_objects::trans_obj::_fcc8a3a1f08fa3a2 ()

No symbol table info available.

#29 0x000000000045f81f in middle::trans::trans_item::_736b03787cae8654 ()

No symbol table info available.

#30 0x0000000000469778 in middle::trans::trans_crate::_5e8b9ab58c8b592f ()

No symbol table info available.

#31 0x00000000005f3df0 in driver::rustc::compile_input::thunk9162 ()

No symbol table info available.

#32 0x00000000005a6998 in driver::rustc::time::_3e691b2a4ba58aee ()

No symbol table info available.

#33 0x00000000005a94dd in driver::rustc::compile_input::_7475af45dcc3eb6c ()

No symbol table info available.

#34 0x00000000005b10ef in driver::rustc::main::_cd8b8c8185af3dee ()

No symbol table info available.

#35 0x00007ffff601e306 in task_start_wrapper (a=0x7ffff511f014) at ./src/rt/rust_task.cpp:176

task = 0x8c1cc0
rval = 42
failed = false
env = <optimized out>

#36 0x00000000deadbeef in ?? ()

No symbol table info available.

#37 0x008c1cc000000000 in ?? ()

No symbol table info available.

#38 0x0000000000000000 in ?? ()

No symbol table info available.

I have not tried reproducing with HEAD yet as HEAD does not build for me right now.