Ristretto 0.0.18
a quirk or a bug?
running Xubuntu Hardy with xfce on Compaq EN Celeron 850

I have come across the following anomaly:

Using Ristretto to open /home/my-name/.thumbnails/normal and then look at the thumbnails [of thumbnails] initially causes all the files found to be duplicated back into /home/my-name/.thumbnails/normal. 
i.e. if there were originally x number of files, that will double to 2x. 
The files newly created have a different 'name' e.g. file:///home/my-name/.thumbnails/normal/5cf9c58f655e8e8b06f045386a45a6e6.png.

Now quit Ristretto, open it again and repeat as above.

What will happen is that again the original x number of files are added into the /home/my-name/.thumbnails/normal folder, making it to now contain 3x number of files. [assuming no other folders containing images were opened in between the first and the second use of Ristretto]

If /home/my-name/.thumbnails/normal initially contains a large number of files [which may well be the case], then the REPEATED use of Ristretto to look at them, will rapidly [and unnecessarily I guess] increase/inflate the size of the folder.

I guess it might be argued that not many users would use Ristretto to access files in the /home/my-name/.thumbnails directory. ;)

I have used gThumb to try and replicate what Ristretto does to /home/my-name/.thumbnails/normal. 
The result was negative, gThumb does NOT cause the duplication I have observed when using Ristretto.
As a further test I used XnView [through Wine], again the result was negative, as with gThumb.