You can enter any min trade size you want on IB's order entry form, and I guess you can also enter any display size you want. So they must have entered a smaller display size than the min trade size. Why would anyone ever want a min trade size as large as 135k? Relatedly, I had a 25k buy limit order at $7 for a junk bond and the last moved from $10 to $4 without hitting my order, so they must have had a min trade size above 25k? Why would anyone do that?