Looked up the rules and the couple of sites I looked at agree with my assumption. Looks like there is a bug in the site's implementation of the variant. Will report 
CrazyHouse
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Feb 10, 2016
0
#2
Feb 11, 2016
0
#3
I tested this and the system would not let me place a pawn on a promotion square.
Was it an actual pawn setting on the 8th/1s rank or a piece that had promoted? Could it be possible they had that piece available to drop?
Feb 11, 2016
0
#4
I don't know, maybe it was just a drop. I was pretty tired when I played. Probably should just chalk it up to that, since the more I think about it, that is probably right.
Probably shouldn't use tactics to win material, shouldn't promote to a queen if it can be taken unless there is an unstoppable mate, and most certainly shouldn't play tired 
how to play this chess with a friend of chess.com. I didn't find any option to challenge a friend for crazyhouse.
May 11, 2017
0
#6
Nothing wrong with promoting to a queen that can be taken. Promoted pawns lose their promotion when captured (according to most rule sets, anyway).
I looked at the game: https://www.chess.com/live/game/1457170864?username=martin_stahl
They didn't drop a pawn on e1 and promote it; they dropped the queen.
A couple comments, BTW:
1. 12. g3 created some serious light-squared weaknesses around the king. Due to the ability to drop pawn chains, light square and dark square weaknesses are a much bigger part of bughouse/crazyhouse than in standard chess. @mastertanCrazyhouse has a good (albeit lengthy) blog post on the subject; a must-read for anyone who really wants to get into bughouse or crazyhouse: https://www.chess.com/blog/mastertanCrazyhouse/light-dark-a-visual-guide-to-crazyhouse
2. Castling can be very risky (note that I said "can be", not "is"). Sacrificing a couple pieces can blow open the king's protective wall of pawns and then you're in trouble. It's often better to keep your king in the center, try to build a strong pawn center, and save the option to castle in case you need to make a quick escape later.
3. You want to push your e and d pawns to control the center, but be careful about any other pawn pushes. Allowing drops on the 2nd and 3rd ranks can be very problematic.
OK, tried CrazyHouse for the first time today. Maybe I made an assumption but shouldn't it be like BugHouse where you can't place a pawn on a promotion square? That is, pawns can only be placed on the 2nd through 7th ranks?
Lost a game to that. If that is supposed to be the rule, I'll have to pay more attention to that in the future.