When working with ufraw (Digital camera RAW image data format coverter) I've noticed that nautilus 2.22.2 shows only generic 'image type' icon for resultant JPEG file. This can be generalised for following scenario:

* some image processing software (ufraw, enfuse) begins by creating empty JPEG file (0 bytes) first and writing data is delayed until time intensive computation is finished (let's say a few seconds) later;
* nautilus assigns generic image file type icon as there is nothing to thumbnail in empty file;
* when data is finally writen to JPEG file a few seconds later, nautilus doesn't  mention and file is never re-thumbnailed.

Perhaps Nautilus is not re-reading the file mtime after it re-schedules 
thumbnailing (during THUMBNAIL_CREATION_DELAY_SECS)?

How to reproduce:

1) find yourself any JPEG file, name it source.jpg
2) open containing folder both in nautilus 2.22.2 and gthumb 2.10.8
3) issue following commands: "touch result.jpg; sleep 5s; cat source.jpg > result.jpg"
4) notice that after 5 seconds gthumb shows result.jpg properly thumbnailed, while nautilus _does_not_ (there is only generic image file type icon on result.jpg)
5) (optional) rename result.jpg to somethingelse.jpg; it gets re-thumbnailed instantly.

Point (4) is the reported problem.