to what i have noticed...this really isnt in portrait mode...but invokes the portrait bug tht n900 has. Notice when using in portrait mode and u close it..the desktop screen is in portrait (bug) mode and quickly reflashes back to normal landscape mode.
Also notice in portrait mode that if u tap the top bar u get the options (clocks & alarms, internet connection, and availability....) in the portrait (bug) mode...

Though an excellent attempt but would like to have a complete and a proper portrait mode..
all kudos to ahockersten and all other team members.