Master slide broken when pptx modified and saved as odp

I have a bunch of proprietary presentations I must use. They all are in pptx format. While they are in language I do not need for my presentations, I want to translate them and then save as odp. All those presentations have thier own master slides. When I open pptx - an original presentation, everything looks fine. When I save the same presentation, with or without changes, master slide appear to be broken and look like large blurry colour areas. And even more - some drawings inside presentation, are distorted - like, originally a small arc, after save in odp - it appear to be huge. I hope that this problem is not because pptx is closed format (hate closed stuff)
Actually the same problem was with older ppt files in OpenOffice 3.2 but disappear in Libre Office 3.6.3.

I have registered it under

Hi @OjarsKrumins,

Sounds like you’ve run across a bug in the way that LO handles pptx files. If installing/running the latest release doesn’t seem to fix this problem, please file a bug and provide a list of steps that can reproduce your problem. The QA Team will be happy to help you track down this issue!

Please post a link to any bugs you file in a comment below using the format “fdo#123456”.