Regarding your question, there are 3 conditions to a raffle/giveaway be completed and winners picked:
be open
not be expired
not be completed
If you don't want people to participate in a raffle/giveaway, then simply don't let them participate by removing the category permission:
You can still add them manually.
You mean, select RAFFLE here:
And not appear GIVEAWAY here:
?
That's it? No, definitely not a bug; that's how it was made. I can hide it in next version if that really annoys you... For now, you can simply ignore it. It's not a required field.
"Don't know when and why" says it all. I can't confirm it. Works fine in my installs. It is saved in a language bit together with category title and description, so I would expect that title and description would be "vanished" sometimes. Do they?
Regarding suggestion, I'll take a look when I'll do a big update... that won't be for now.