It seems so obvious it has shocked me twice now.

[KageTensai]

Why do I die when I shrine or FO if I'm in rage and my HP would drop to 0 if I cancelled rage? This is pointless and frustrating and really doesn't make any sense. If there's some exploit that would exist if it didn't, I'll shut up.

[BurningDownTheHouse]

Nah, just an everlasting bug.
It's hilarious when it happens though. :D

[Crazyfruit]

It happens with the rage spell too, or taking off your con item to put on a haggle one at the vendors :D

[Gol]

You get stripped of buffs before you get SP/HP recovery. At that time, you dip below -10 and die.

[Shaamis]

when you rage, you get the adrenaline rush, hence the HP boost from teh boos tin CON.

When you come out of the adrenaline rush/rage, your CON goes down to the normal level, and you lose the HPs gained by it.

If you dont take the time to drink a heal pot, and make sure you dont collapse after coming out of a rage, sure, your HPs will go to negs, and you might die.

This is working as intended from what I remember in PnP.

Barbarians in PnP go on the history of these great warriors collapsing and almost dieing after great battles, where they were in a rage-like effect, why not in DDO too?

just drink a heal pot, or ask for a heal spell to be cast on you before you die.

[Impaqt]

Not really a bug. Just the way resting works.

Equipt a +HEAL item to increase the amount of healing the shrind gives ya. Drink a Pot before shrining. WHen you rest, your Con Buffs go away. you need to make sure you can survive the loss of the buff.

[Missing_Minds]

Per Rage: The increase in Constitution increases the barbarian’s hit points by 2 points per level, but these hit points go away at the end of the rage when his Constitution score drops back to normal.

http://www.d20srd.org/srd/classes/barbarian.htm#rage

Working as intended and has been for years.