@Michael: Yes, that is correct for my laptop, which I'm currently using. I have also had this issue on my desktop computer running a fresh install of Ubuntu Precise during development (starting January 26th 2012, to be exact - see comment #11). I did not have any issues on Precise with it before that date, and I continue to have no issues with it on my desktop's 11.10 partition.

Here are my steps to reproduce the problem on Precise, as clearly as I can make them:
1. Open Simple Scan. For my scans, I normally use Text mode from the drop-down menu next to the Scan button, though I haven't tested the issue with Photo mode. Simple Scan remembers whether you used Text mode last time, so if you already had it set to that from a prior run, then there is no need to set it again.
2. Have a few multiple-page documents ready to scan for the rest of these steps.
3. Scan in the first document by placing each page in succession on the glass and pressing the Scan button to scan it in. After each page finishes scanning, remove it and place down the next one before pressing Scan again. This is simply normal usage of the scanner.
4. When you have finished scanning the entire document, you may choose to press the Save button to save your document first, though I don't think this is necessary to trigger the bug. Whether you do that or not, you will next want to click the leftmost button in the toolbar (its tooltip says "Start a new document") so the previous pages are cleared out of Simple Scan and you can start scanning the next document. *Up to this point, there should be no issues, regardless of how many pages are in the first document scanned.*
5. Repeat steps 3-4 above as you normally would with your other documents. Now, on any given page at random (not necessarily the first couple you scan, IMO it is most likely to occur on the second page of the second document or the ones following it), after you place the document on the scanner and click the scan button, the scanner head will start moving across the scanning bed as usual, but Simple Scan will briefly freeze with the spinner over the next page to be scanned appearing stuck as soon as the head starts moving, and then it will crash and close shortly before the scanning head can finish moving to the end of the glass. The scanning head will remain stuck at the end until you either:
- Turn the scanner off and turn it back on
- Reopen Simple Scan from the Dash
...at which point it will return to its initial position and you can resume scanning as usual until the bug is triggered again by following steps 1-5.

No other actions (i.e. page re-ordering or cropping) are followed when performing the above steps.

For me, this bug is relatively well-reproducible. It does not always show, but having longer documents, each of length 3 pages or more, increases your chances of seeing this bug. I would estimate that in practice I encounter it roughly 90% of the time. Note that the crash for me only seems to occur on or after the second page of the second document scanned before Simple Scan is closed, though the exact page when the crash will occur appears entirely random. In other words, repeating the same steps above with the same documents does not necessarily produce the crash at the same page every time. I may be able to avoid the crash if the documents I'm scanning are short and I can get them all scanned and saved before the crash can occur.

The impact of the crash on the user is simply that the current document being scanned is lost and must be started over when Simple Scan is re-opened. Documents already scanned and saved are not affected. Pages scanned before and after the crash are not visually affected in any way. The scanner itself does not appear to be negatively affected, other than temporarily staying stuck at its end position until it is used again.

The only sure-fire workaround I have to avoid this crash, as I previously mentioned in comment #12, is to close and re-open Simple Scan in between all documents. That is, after I finish scanning all the pages in one document and save it, I close Simple Scan, then re-open it from the Dash or by some other method, then scan and save all the pages for my second document, close and re-open Simple Scan before proceeding to the third, etc. As one might imagine, this is not a very efficient way to use the program, but it avoids the risk of trying to scan multiple documents at once only to lose all of your work after the last saved document when you least expect it.