We checked it already and as you said, the problem is with download manager plugin. This plugin call plugin’s icons, the same as our theme do and that`s why all plugin’s style overwrite our styles. We recommend to contact with plugin’s author because there is nothing what we can do with this thing.
I have one more question, I changed my theme, but when activating the plugin download manager, all my icons disappear (eg shopping cart, arrows, etc.), you can fix this error? ๐