To confirm (18 months later) - this is still the way the catalyst app works. I'm not sure why it does not take the "unspent" staking rewards into account, it would seem like a pretty sensible idea for it to include them. However, Daedalus users will need to make a transaction to claim the staking rewards into the main wallet.
You could, for example, send a couple of Ada to Coinbase, Binance, etc. You can always send them back if you want to. You'll notice the wallet balance in Daedalus will update and the "unspent rewards" will change to 0.
It's not clear how quickly the Catalyst app will refresh the wallet balance though - I assume it doesn't refresh on a regular basis but I have no doubt that the snapshot will be correct when it takes place.