Transparent custom logo has black background

Hi,

Here is some weird behavior in Zoho.

I have a custom logo for my domain with a transparent background and it looks good in the tabbed business view for all apps when I log into business.zoho.com or personal.zoho.com. When I log directly into mail.zoho.com, writer.zoho.com, etc, the background is black. I've attached screen shots showing what happens.

Henry