bash crashed with SIGSEGV in internal_malloc()

I was typing on the command line and backspacing and BOOM the shell (and enclosing rxvt) went away.
I can't ever remember crashing bash before.
I had noticed yesterday that this interactive bash had managed to use up way more cpu (over 30 minutes!) than my other two dozen bash shells in various windows:

bash DX idallen pts/3 1097.12 secs Tue Apr 17 01:52

The nearest bash in CPU use was 6 *seconds* of CPU. What is with this one?

I've also had Firefox crashes, so I'm not above believing that I have either memory issues (but memtest says I don't) or SSD issues (OCZ Vertex 2).

ProblemType: Crash
DistroRelease: Ubuntu 11.04
Package: bash 4.2-0ubuntu3
ProcVersionSignature: Ubuntu 2.6.38-13.57-generic 2.6.38.8
Uname: Linux 2.6.38-13-generic x86_64
Architecture: amd64
Date: Tue Apr 24 17:26:16 2012
ExecutablePath: /bin/bash
InstallationMedia: Ubuntu 11.04 "Natty Narwhal" - Release amd64 (20110427.1)
ProcCmdline: -bash
SegvAnalysis:
 Segfault happened at: 0x4a9d6b: callq 0x41ae20 <memset@plt>
 PC (0x004a9d6b) ok
 source "0x41ae20" (0x0041ae20) ok
 destination "(%rsp)" (0x7fff9e2cbf70) not located in a known VMA region (needed writable region)!
 Stack memory exhausted (SP below stack segment)
SegvReason: writing unknown VMA
Signal: 11
SourcePackage: bash
StacktraceTop:
 ?? ()
 xmalloc ()
 ?? ()
 rl_vi_change_to ()
 _rl_dispatch_subseq ()
Title: bash crashed with SIGSEGV in xmalloc()
UpgradeStatus: No upgrade log present (probably fresh install)
UserGroups: adm admin cdrom dialout disk lpadmin plugdev sambashare video