He gained 100K minus taxes in his taxable a/c.
Thinking this "investment" was a sweet deal and seeking to save on taxes, he closed the fund in his taxable a/c then put down 300K back into the same scheme with mlney in his IRA, losing 80% of that (240K)
In effect, his total "investments" were 500K, with a net loss of (-) 240K + 100K or (-) 140K + taxes he paid on a gain of 100K in his taxable.
He banked the "gain" in the taxable, paying taxes on it, no doubt, and then ate the loss in his IRA. The trustee is now trying to clawback another 50K of the gain out of him, failing which they're planning to sue him for the entire 100K gain on taxable. If he forks over the 50K, then he is increasingly his net loss to 190K + the taxes already paid on the 100K "gain".
There must be a legal reason that the bankruptcy trustee is treating his taxable & IRA as two different investments, even if he owns both of them. What he needs is a securities lawyer and a pitbull CPA in his corner. I doubt laypeople can figure out why the trustee is allowed to legally demand money back, even if it increases OP's losses to almost 200K!