When you die and you perss escape (regardless what you do afterwards, equipscreen, rulescheck, start a poll etc) you don't get xp.
This was implemented due to many people at siege who spawned, died and went afk. Perfect leeching without any chance to see whether the person went afk midround or was just actively leeching.
Only chance to get rid of that was by changing the system so that you don't get any xp/gold when you press escape. Now people spawn again on siege and get killed and after some time qml'ed or kicked by admins.
Alt+tabbing out of the game when you are dead is no problem, as long as you don't press escape beforehand.
Alt+tabbing might cause crashed, especially when you do it too often (and it seems especially when you have a multi
)
Alt+Enter for windowmode works better and reduces crash chance (can still happen)
As far as I know it's not related to one's pc. It's just mount and blade and it's crappy engine