Hello there,
with Bolt 1.2.1 there was a problem with thumbnails being not shown especially on 1&1 webspace. I found a solution in github here:
https://github.com/bolt/bolt/commit/089787d562e0a0a820e8c39e8874f03e320118cd
Now in 1.3.1 it is again that thumbnails being not shown like above on 1&1 webspace. It seems that while a fix is included in the new timthumb, it is still necessary to switch the order of REQUEST_URI and REDIRECT_URL to make thumbnails work.
I don't know if this a unique case....