Easiest to see using a table with headers in gtk-demo, but also fails for other tables with headers that are children of the table.

1) Download the attached zip file and Python script. (Don't unpack the zip.)
2) Run gtk-demo.
3) Run the Editable Cells demo under Tree View.
4) Run the attached Python script with the zip file in the same folder.
5) Move the mouse over the cells in the table. Notice the information by the Component interface on the table widget is off by one row.
6) Move the mouse over the headers. Notice the cells below the headers are reported, not the headers themselves (i.e. it's still off by one row).

Also, the behavior of getAccessibleAtPoint is inconsistent once the table has been scrolled and resized. Sometimes, the reported cell is incorrect in both row and column after the scroll.