Surprise attacks seem broken

[Gadzooks]

So I sneak up on a sleeping bugbear

Attack them, hitting them pretty hard, but not killing them.

Combat starts
Im told the bugbear is surprised. (Shouldnt that mean the bugbear cant attack?)
Im told its my turn.

From the DnD 5e rules:
"If you're surprised, you can't move or take an action on your first turn of the combat, and you can't take a reaction until that turn ends. A member of a group can be surprised even if the other members aren't."

More so, my character still says they dont have enough action points left to do anything, which also makes no sense as I did the sneak attack outside of combat.

So I have to end my turn

The bugbear stands up (movement), and attacks me (action), neither of which they should be allowed to do if they are surprised.

Am I missing something here, or are the game mechanics not working as they should?

[HozzMidnight]

Surprise seems bugged. I am level 5 in the Underdark and I literally just got my first surprised enemy despite opening every combat I can the same way, shooting someone from stealth with my Ranger.