This appears to have appeared in or after revision after #36608

The ace:dataTable deselection in this showcase example is quite obviously bugged after a brief attempt at using it, as QA puts it:

I am fixing the testcase for ace:dataTable - Row State and noticed that once a row is selected it can not reliably be deselected by clicking on it again. Example 1:
Click on one row, then click on it again. The highlighted color of the row does not change to a deselected look and the name of the row remains in the controls:selectedRows area.

Example 2:
Click on Enduro row.
Click on Swordfish row.
Click again on Enduro Row.
Enduro row does not appear deselected but its row name is removed from the controls:selectedRows area.
Click on Swordfish row
Swordfish row becomes deselected, its name is removed from controls:selectedRows.
Enduro remains selected.

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After turning on DOM Diff debugAB the problem becomes more apparent. Watching carefully, debugAB output will be thrown for the navigation to the example, as expected, but the first selection on the example doesn't cause debugAB output. Subsequent requests do, but the old DOM of these diffs don't match the client, the selection is not in it, so deselections are not applied to the client.

The update that returns from the selection request that fails to diff updates the entire table component, as well as the entirety of a separate button form, inexplicably for a single row selection.

I think this may have something to do with onElementUpdate work that is ongoing.