Steps to reproduce:
1. for simplicity: start with a new gnucash file - File->New->New File;  use defaults in new file setup druid

2. Begin importing QIF file;  File->Import->Import QIF

3. select any QIF file;  doc/examples/web.qif in svn will work as well as any

4. Press "Forward" button
  Heading is now: "Set the default QIF account name"
  if using web.qif, "Account name" textbox is set to: "web"

5. Press "Forward" button
  Heading is now: "QIF files you have loaded"

6. Press "Forward" button
  Heading is now: "Match QIF accounts with GnuCash accounts"

7. Press "Back" button button repeatedly until
  Druid Heading is again: "Set the default QIF account name"
  "Account name" textbox is still set to: "web"

8. Change "Account name" textbox value to "web1" (or any other different value)

9. Press "Forward" button

gnucash crashes here immediately with backtrace

Stack trace:
Backtrace:
In unknown file:
   ?: 0* [qif-import:fix-from-acct #f "web3"]
In /opt/gnucash/share/gnucash/scm/qif-import/qif-dialog-utils.scm:
 558: 1* [for-each #<procedure #f (xtn)> ...
 562: 2*  [qif-file:xtns #f]
In unknown file:
   ?: 3   (and (eq? (quote #) (record-type-descriptor obj)) (struct-ref obj 2))
   ?: 4*  [eq? #<record-type qif-file> ...
   ?: 5*   [record-type-descriptor #f]
   ?: 6    (if (struct? obj) (struct-vtable obj) (error (quote not-a-record) obj))
     ...
   ?: 7    [scm-error misc-error #f "~A ~S" (not-a-record #f) #f]

<unnamed port>: In procedure scm-error in expression (scm-error (quote misc-error) #f ...):
<unnamed port>: not-a-record #f


Other information:
this bug exists in Debian Lenny (testing) also (version: 2.2.1-1), and reported in  Sid (unstable) too.  it is reproduceable with every qif file I tried.  It was reported in irc that you only need to move one step past the "Set the default QIF account name" druid step to repro, as long as you move back and forth a couple times...  suggesting that the magic needed is something like: "press the Back button at least twice".