S class PE becomes H when moving through booking process?

Trying to book an S class PE fare NYC>LHR return, for upgradeable option. and despite knowing my way around the system, I thought, and using the specific page for upgradeable fares:
http://www.virgin-atlantic.com/en/gb/fr ... sp?ad=AFF1
I find my S flights/price combo, and proceed to try and book it, moving onto the 'flight Itinerary' page it looks the same, but if you click the outward/return tabs, (and many might not bother) it has changed into an H! Which is not upgradeable, of course.
Is this a system anomaly, is the first booking page, where I selected selecting S, right? or the later one's outbound/inbound tabs - where it switches to saying its an H?
http://www.virgin-atlantic.com/en/gb/fr ... sp?ad=AFF1
I find my S flights/price combo, and proceed to try and book it, moving onto the 'flight Itinerary' page it looks the same, but if you click the outward/return tabs, (and many might not bother) it has changed into an H! Which is not upgradeable, of course.
Is this a system anomaly, is the first booking page, where I selected selecting S, right? or the later one's outbound/inbound tabs - where it switches to saying its an H?