I figured that! 😉
The problem is consistent from all pages including acs-admin as well as non-admin pages.
As far as I can tell, my kernel parameters look fairly sane and the problem occurs with ForceHostP set to 0 or 1. Are there any I should particularly be looking at?
Incidentially, I noticed that the upgrade from 5 to 5.01 reset ForceHostP to 0 (as well as overwriting my customised acs-subsite/www/index.adp file).
