crash suggestions

[Dan]

I'm having a crash I've been unable to figure out. I have a small 
pretty print function that so far has handled most of my needs. 
However while debugging I threw something at it that caused a 
crash, so I know it must have an issue.
The portion calling out to pp is
---
     double getRate(double taxableGrossIncome) const {
         auto sortedRange = assumeSorted(_table[]);
         auto needle = KeyValuePair(taxableGrossIncome, 0);
         auto found = sortedRange.lowerBound(needle);
         if(!found.empty) {
             writeln(pp(found)); // fine
             writeln(pp(found), taxableGrossIncome); // fine
             writeln(taxableGrossIncome, pp(found)); // crash
             return found[$-1][1];
         }
         return 0;
     }
---
I can call writeln(pp(found)) or writeln(pp(found), 
taxableGrossIncome), but if I try writeln(taxableGrossIncome, 
pp(found)) I get a  seg fault in snprintf inside of 
format.formatValue. It is strange to me that it is the order of 
args that causes the crash.

- I don't use new/delete anywhere. I do have one branch of code 
which checks against a pointer to print and derefences it if not 
null.
- In gdb before the snfrpintf call, the value to be printed is 
available, so my guess is somehow the local buff variable on the 
stack is corrupt?
- I ran through valgrind when I commented out the offending line 
and did not see anything unreasonable.
- pp creates an appender and passes it through to pprint with 
what to print and that is where formatting occurs. Maybe my 
creating a appender on the stack, appending to it, and then 
returning the contents with '.data' is not allowed/safe and for 
all my other uses I'm lucky?
- Between the 7th frame and 8th is where something goes wrong. 
The weird thing is that gdb lists the print function as having a 
this paramenter in addition to the two I specified. Not sure how 
that is happening?

So, I'm looking for advice on anything obviously wrong, any 
tricks of the trade that might help me track it down, what 
standard rules am I violating, etc.
The single file with main causing the crash is at: 
http://pastebin.com/M67PamQM
Also the call stack is below. Any suggestions appreciated.

Thanks
Dan

Program received signal SIGSEGV, Segmentation fault.
0x00007ffff764990a in snprintf () from 
/lib/x86_64-linux-gnu/libc.so.6
(gdb) where
#0  0x00007ffff764990a in snprintf () from 
/lib/x86_64-linux-gnu/libc.so.6
#1  0x0000000000433533 in 
std.format.__T11formatValueTS3std5array17__T8AppenderTAyaZ8AppenderTxdTaZ.formatValue() 
(f=<error reading variable>, obj=50000, w=...) at 
/usr/include/dmd/phobos/std/format.d:1478
#2  0x0000000000433132 in std.conv.__T5toStrTAyaTxdZ.toStr() 
(src=50000) at /usr/include/dmd/phobos/std/conv.d:99
#3  0x00000000004330e8 in std.conv.__T6toImplTAyaTxdZ.toImpl() 
(value=50000) at /usr/include/dmd/phobos/std/conv.d:824
#4  0x00000000004330cc in std.conv.__T2toTAyaZ.__T2toTxdZ.to() 
(_param_0=50000) at /usr/include/dmd/phobos/std/conv.d:268
#5  0x000000000043305c in 
std.conv.__T8textImplTAyaTxdTAyaZ.textImpl() (_param_1=..., 
_param_0=50000) at /usr/include/dmd/phobos/std/conv.d:3060
#6  0x000000000043301b in std.conv.__T4textTxdTAyaZ.text() 
(_param_1=..., _param_0=50000) at 
/usr/include/dmd/phobos/std/conv.d:3042
#7  0x0000000000432fe1 in 
e.__T5printTS3std5range73__T11SortedRangeTAxS3std8typecons14__T5TupleTdTdZ5TupleVAyaa5_61203c2062Z11SortedRangeTS3std5array17__T8AppenderTAyaZ8AppenderVAyaa1_20VAyaa0_VAyaa1_0aZ.print() 
(this=0x0, t=0x7fffffffd8b0, appender=...) at /tmp/e.d:69
#8  0x0000000000432ecd in 
e.__T5printTS3std5range73__T11SortedRangeTAxS3std8typecons14__T5TupleTdTdZ5TupleVAyaa5_61203c2062Z11SortedRangeTS3std5array17__T8AppenderTAyaZ8AppenderVAyaa1_20VAyaa0_VAyaa1_0aZ.print() 
(this=0x0, t=0x7fffffffd8b0, appender=...) at /tmp/e.d:31
#9  0x000000000042d93e in 
e.__T5printTS3std5range73__T11SortedRangeTAxS3std8typecons14__T5TupleTdTdZ5TupleVAyaa5_61203c2062Z11SortedRangeTS3std5array17__T8AppenderTAyaZ8AppenderVAyaa1_20VAyaa0_VAyaa1_0aZ.print() 
(t=0x7fffffffd970, appender=...) at /tmp/e.d:31
#10 0x000000000042d39d in 
e.__T2ppTS3std5range73__T11SortedRangeTAxS3std8typecons14__T5TupleTdTdZ5TupleVAyaa5_61203c2062Z11SortedRangeVAyaa1_20Z.pp() 
(item=0x7fffffffd970) at /tmp/e.d:93
#11 0x000000000042c482 in e.TaxTable.getRate() 
(this=0x7fffffffd9e0, taxableGrossIncome=50001) at /tmp/e.d:116
#12 0x000000000042c88e in D main () at /tmp/e.d:131
#13 0x000000000043a1f4 in rt.dmain2.main() ()
#14 0x00007fffffffdbe0 in ?? ()
#15 0x00007fffffffdac0 in ?? ()
#16 0x0000000000439b6e in rt.dmain2.main() ()
#17 0x0000000000000001 in ?? ()
#18 0x0000000000000016 in ?? ()
#19 0x000000000066a020 in ?? ()
#20 0x00007fffffffdbe0 in ?? ()
#21 0x00000000ffffffff in ?? ()
#22 0x0000000000000000 in ?? ()
(gdb)