There's nothing in the actual window file that is telling it to open to a different tab. What you want to edit is your character's uisettings file. They're named on the template of "Server_Character_eq2_uisettings.xml."
Try searching for
Code:
Window Name="Persona"
and then under that where it says
make sure that it's 0 there and not some other number. I believe the page= controls which page was last open, and 0 should be the topmost (inventory/equipment) page.