I've dabbled in deeply discounted corporates (junk bonds) at IB. Liquidity sucks. The broker has to make their own market. So sometimes you will see bonds trade at or better than my limit on TRACE but IB still doesn't fill. Basically, some other broker-dealer had inventory at your strike but IB didn't. I imagine Treasuries are the same way. But weird that they would have deep inventory of the most liquid security in the market?
If you contact them, please post findings here. I'm interested to know what the story is.
Didn't contact them, but this is what I did:
Instead of clicking "close" to populate the order form, I manually entered the CUSIP. The CUSIP is different from the IBCID interactive brokers uses to identify the bond in my account.
When I placed the order this way, I got a notice "your order is too small to trade at NBBO - please increase size or more aggressively price". So I increased size to 5, same message. So I increased size to 10, filled instantly at a competitive price (somewhere between bid/ask).
So I'd say it definitely was a problem with selling too few bonds at a time, and possibly an additional problem with identification of the bond. I don't know the size it needs to be, if less than 10 that's nice since I'm selling bonds to fund expenses and I don't want a bunch of extra cash that could be earning interest at a rate higher than IB commissions. I had decided to just sell every 1-2 months, but it looks like for bonds it'll have to be less often.
This lesson only cost me $50 (bonds are down today, yo)