Charged for more than quoted price in paper trading

In Paper Trading, I bought 5 shares of AMHCU at a quoted price of $10.17 per share for a total of $50.85. When I looked at the order history, I was charged for $4294.67 per share!

Is this a bug in Paper?

In its entire lifetime AMHCU has never been above $12 so it’s not a problem with the quote being out of date.

The price is displayed normally in the positions view, but it looks like I’m down $21k, which is frustrating.

I noticed this happened yesterday with the same stock, so perhaps it is related to specific stocks.

I asked this question on Slack and got a great answer from @Dan_Whitnable_Alpaca

Paper trading prices are based on bid/quote prices. For very thinly traded stocks, or in this case units, those bid/quotes can be just something that someone has hanging out there and can be very unrealistic. There were fewer than 300 shares of AMHCU traded today and that looks like it was in 3 trades. It’s not surprising that nobody has realistic quotes. You’ll often see this low volume when trading units.
This does highlight an issue that one should address in live trading. Be aware of the current bid/ask before placing a market order. More than likely a buy will fill around the ask price. It’s typically a good practice to place limit orders. Limit orders which are priced within the NBBO spread are treated like market orders but also have the benefit of your limit.

There are limits to how well paper trading simulates live trading. Less liquid low volume securities aren’t simulated very well in paper trading.