Stocks down 10% cant be shorted?

I have a question regarding equities that had a 10% drop, my broker places a little red circle around them to warn that the security cannot be shorted. Yet, if you try to, you can actually short them and get filled. Question to those with experience, is this illegal? Can you get penalized ? Not sure how this works, why provide the warning that the security cannot be shorted yet you can actually borrow shares to short it, very confusing.

Thank you.

 

https://www.interactivebrokers.com/en/index.php?f=am_stockshorting&p=overview3&conf=am

 

If there are options available you can use them to simulate a short position

 

You can't place marketable orders - you have to place limit orders and wait for someone to hit you.