Retirement tax questions

That was my understanding also, but today I got a call from my broker saying I owed 5 figures in taxes for UBTI on a Roth IRA because I sold some shares last year.  I don't understand, my total profit was less than half of what my broker is saying I owe in taxes and my K1 box 20 V is less than 1/5 of what my broker says I owe in taxes.  

 

I requested a copy of the 990-T and it makes no sense.  I insisted the 990-T was not correctly completed, but no luck.  

 

Is this even possible where I made small profit on stock, but the taxes I owe are over twice my profit so it is basically a loss?