For one, when the card was created, the only way to make a Lost Soul leave play would be to discard it.
To your actual question, cards like Jephthah and other "per game" abilities are special. From the REG:
"A 'per game' ability applies to all copies of the card and is not reset (e.g., return to pile)." (Miscellaneous)
Otherwise, every card completely resets upon hitting the hand, deck or discard pile:
"Cards returned to a draw or discard pile return to face value unless the card has limited game use (e.g., Burial Shroud)." (Return to Deck)
"Cards returned to hand return to face value." (Withdraw from Battle, Default Conditions)