As per my understanding based on the configuration mentioned, i think there is a refresh call missing after the pyExpanded property is set to false. Could you trying adding a refresh button/icon above the grid and after the row shows as collapsed, try manual refresh (just for testing purpose) and let us know your observations.
I tried the way you said. Its working if I click on button.
My another observation is (without refresh button), After clicking on save that Icon will collapse but not the row, As soon as clicking save button , If I click outside of that button Row is refreshing.
This behaviour is there for all Grid in entire application (it was working in 7.1 but not 7.2.2 CSHC 7.1 FW) where we used "pzModalButton". On click of button I did Refresh section and Run DT (Please find attachment for configuration I did). Neither of them executed.
Can you please check below link. May be the same behaviour.