Hi, thank you for your bug report! The proxies are very provisional, so they may not always work well. Adding a "use uniform material" checkbox is a good idea, I have added it to my list of smaller feature requests. Can you please send me the .cgeo file, and perhaps also the .pln file? That will be the easiest way for me to debug this.
(I also moved this post to the "bug reporting" section of the forum.)