Whats your video memory?

From what I can see the program runs out of address space....which is unusual because 64 bit can hold more than 32 bit

256M.
Also, it drops core dump when enabled with ulimit.

Simon,
It works in strange way: sometimes crashes, sometimes not. With same errors.
P.S. lin64 binary archive contains 32 bit versions. It is OK?
% file powder-64-sse2
powder-64-sse2: ELF 32-bit LSB executable, Intel 80386, version 1 (SYSV), dynamically linked (uses shared libs), for GNU/Linux 2.6.18, stripped

Edit: 32 bit version works always OK.

Simon,
Yes. Crashing in free() or realloc().

Both are functions concerning the drawing

I do not know, I'm not a dev :)
But some of information can be received with gdb:

Core was generated by `./powder.debug scale:2'.
Program terminated with signal 6, Aborted.

#0 0x00007fa92af48e7e in raise () from /lib64/libc.so.6
#1 0x00007fa92af4bd00 in abort () from /lib64/libc.so.6
#2 0x00007fa92af7e8fd in __libc_message () from /lib64/libc.so.6
#3 0x00007fa92af88156 in malloc_printerr () from /lib64/libc.so.6
#4 0x00007fa92af8ca9c in free () from /lib64/libc.so.6
#5 0x000000000042badf in http_async_req_status (ctx=0x24557c0) at http.c:487
#6 0x000000000042bc7c in http_async_req_stop (ctx=0x24557c0, ret=0x7fff3cdd95ec, len=0x0) at http.c
:532
#7 0x000000000042bfef in http_simple_get (uri=0x24575b0 "http://powder.hardwired.org.uk/Tags.api?ID
=2956", ret=0x7fff3cdd95ec, len=0x0) at http.c:620
#8 0x0000000000422f2d in search_ui (vid_buf=0x7fa92ba8e010) at powder.c:6452
#9 0x0000000000429374 in main (argc=2, argv=0x7fff3cdd9ad8) at powder.c:7968

Maybe this will be helpful. I'm not a developer, so I have only basic debugging skills :X