Steve/Niklas,
This is what I get when trying to open the default.xsp (tried on a local 8.5.1 client and on a 8.5 FP! server)
Unexpected runtime error
The runtime has encountered an unexpected error.
Error source
Page Name:/default.xsp
Property: beforePageLoad
Exception
Error while executing JavaScript action expression
Script interpreter error, line=58, col=12: Reference error: '@ClientType' not found