I noticed that when turning on Site Detection Management and redirecting to a mobile page/site, that some of the styles were not showing up. However, they show up if you delete or disable mobile site redirects. After some investigation, it occurred to me that the default skin.css file was not being loaded, but css files that were registered with client resource management were being loaded. So to solve this bug, I put the following in my skin ascx file.

<%@ Register TagPrefix="dnn" TagName="STYLES" Src="~/Admin/Skins/Styles.ascx" %>

...

<dnn:STYLES runat="server" ID="SkinCss" Name="SkinCss" StyleSheet="skin.css" UseSkinPath="true"/ >

 

I have no idea what causes this, but it is certainly puzzling since it works sometimes and not other times depending on the device and mood of the gods.