Hello,
Sorry to hear you are having issues. I tested on my system and it look okay on my system. Refer screenshot below.

So, there are few possibilities of your issue. Let try one step at a time. First, need to make sure if Windowblinds was properly installed. 

Please try, uninstall Windowblinds, reboot immediately when uninstall is done(important), download latest version available in your account product download page: https://store.stardock.com/myaccount/products . Install it, reboot immediately again. Retest it and report back.

Thank you.
Basj,
Stardock Community Assistant.

Something might get corrupted, does the issue only happen on Aero 11 skin? Is the issue appear on any other skin? If not, please delete the Aero 11 skin from your library and redownload, and reapply it. Retest and report back.

Thank you,

Basj,
Stardock Community Assistant

Does it also effect Arcylic 7 which come along with Windowblinds when you installed Windowblinds.

Thank you,

Basj,
Stardock Community Assistant

If you don't have Acrylic 7 in your WB Skin list, Diamond is also one of Skin that come with WB.

Thank you,

Basj,
Stardock Community Assistant

That show, most probably, issue with the skin itself. Do you know how to use Skinstudio? If you do, please edit this section and see if it help with your issue.

Thank you,

Basj,
Stardock Community Assistant

This, said that he don't have issue with Diamond, no?

Thank you,

Basj,
Stardock Community Assistant

To delete a theme, apply a skin that you are not deleting, once that is done, right click on the theme you're trying to delete and select "Delete Style". To reinstall, redownload the style from Wincustomize.com. Double click on it. And the theme should reinstall.

Thank you,
Basj,
Stardock Community Assistant.