ASSERT (1.8.0-8 adobe reader 9.5) "stats expect primary==DR's num" in shadow light mode

_From [bruen...@google.com](https://code.google.com/u/109494838902877177630/) on September 15, 2014 22:40:07_

Running Adobe Reader 9.5 on XP64 in shadow light mode
hits an assert. The assert is right after the window is rendered.
I did have a custom allocator set up but it should be unrelated (will
confirm):

% ~/drmemory/kraken/build_x86_dbg/bin/drmemory.exe -dr_ops "-msgbox_mask 12" -pause_at_assert -dr e:/derek/drmemory/kraken/exports -no_skip_msvc_importers -no_check_uninitialized -no_count_leaks -exit0 -batch -- ./AcroRd32.exe E:/derek/i1384-custom-malloc/tiny.pdf
~~Dr.M~~ Dr. Memory version 1.8.2069

ASSERT FAILURE (thread 384): D:\derek\drmemory\git\src\drmemory\syscall.c:527: sysnum == sysnum_full.number (stats expect primary==DR's num)

0:000> .frame 5
05 19ddedcc 73a966c8 drmemorylib!event_post_syscall+0xbdb [d:\derek\drmemory\git\src\drmemory\syscall.c @ 527]
0:000> dv
drcontext = 0x19d991c0
sysnum = 2
mc = 0xcccccccc
syscall = 0x73d5e644
pt = 0x19de5390
sysnum_full = struct _drsys_sysnum_t
0:000> dt sysnum_full
Local var @ 0x19ddedbc Type _drsys_sysnum_t
+0x000 number : 4149
+0x004 secondary : 0
0:000> ?? _(drmemorylib!syscall_info_t_)syscall
struct _syscall_info_t
+0x000 num : _drsys_sysnum_t
+0x008 name : 0x73d55f3c "NtUserDispatchMessage"
+0x00c flags : 1
+0x010 return_type : 5
+0x014 arg_count : 1
+0x018 arg : [18] _sysinfo_arg_t
+0x180 num_out : (null)
0:000> U user32!NtUserDispatchMessage
USER32!NtUserDispatchMessage:
7d949146 b835100000 mov eax,0x1035
0:000> ?? 0x1035
int 4149

syscall # 0x0002 12 args fixup 0x00 = NtCallbackReturn

seems like a DR bug: why didn't the dcontext swap have the proper
dcontext->sys_num?

_Original issue: http://code.google.com/p/drmemory/issues/detail?id=1628_