Clustering SE in an Instrumental Variable (IV) regression yields to negative effects compared to "unclustered" IV regression - How's that?

Hello


today I performed an IV regression with two instruments. Both instruments are indicator variables (dummies). At some point, I felt the need to cluster the SE by individual - and all over sudden- the effects of the instrumented variables changed direction. I thought only Standard errors change.

How can that be?

I try to make a similar example using dataex, but so far I am loosing...

Thank you!