Some associate product not showing image of configurable product

Question

Some associate product not showing image of configurable product, you can see the error in this page: https://www.cammaleao.com/ankle-boot-oxford-wirth-couro-taupe.html

In "Escolha seu tamanho" please choose number 39 (not show images), after choose 33 (show images). Both associated products are similar. I am trying to debug with chrome/firebug... But I have not succeeded.

I tried flush all types cache, including "Catalog Images Cache".

Any suggestions? Thanks in advance.