Creating a brand new app with no customization, I've added a table, enabled expandable rows and added a form component to the expanded row.
The form in each expanded row should show data from the selected row but as you can see here the form in the second row is populated with the data from the first row:
But if I close the expanded row and then reopen it, the correct info is displayed:
Open the second row and the form is filled with the data from the previous row:
Apparently, you have to click the row first and then click the expanded row icon which in effect it takes two clicks on the selected row for the form to use the selected rows data. I haven't customized the table or the form at all, this is straight out of the box.
I've posted about similar behavior here but that post has yet to be reviewed.