RP mdui DisplayName only shows when at least one letter is uppercase

Sorry, I didn't look much at this at the time, but this is being caused by the somewhat odd control logic we included.

It only displays if the SP's entityID doesn't contain the service name, so what happens is your lower case display name must match part of the entityID and blocking the display. You can change that freely, it's your page.

The default there is because the RPUI code returns the hostname from the entityID as a fallback if there's no name to use. So it's not an equality check and I didn't want to do weird parsing just for this example.

Agreed..
We have only a very minimal modification of that area of the login.vm

Stock...

49 #set ($serviceName = $rpUIContext.serviceName)
50 #if ($serviceName && !$rpContext.getRelyingPartyId().contains($serviceName))
51 <legend>
52 #springMessageText("idp.login.loginTo", "Login to") $encoder.encodeForHTML($serviceName)
53 </legend>
54 #end

Ours...

82 #set ($serviceName = $rpUIContext.serviceName)
83 #if ($serviceName && !$rpContext.getRelyingPartyId().contains($serviceName))
84 <legend>
85 ## Begin: UCB Edit - bold the service name with strong tag
86 #springMessageText("idp.login.loginTo", "Login to") <strong>$encoder.encodeForHTML($serviceName)</strong>
87 ## End: UCB Edit - bold the service name with strong tag
88 </legend>
89 #end

I have a hard time imagining how that's even possible, but no, it's not intentional.