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Are you using the "estimated metadata" option?

Yes, and turning that off in the connection settings "fixes" the query count issue. As I recall, not using the estimated metadata imposed severe performance penalties on larger tables. Is the "estimated metadata" not compatible with the query test? In other words is this a bug or a limitation that cannot be overcome? If the latter, the test button should probably be unavailable if the estimated metadata setting is turned on, perhaps with a tooltip that says as much if you hover over the grayed-out button in the GUI.

John Tull wrote:

Yes, and turning that off in the connection settings "fixes" the query count issue. As I recall, not using the estimated metadata imposed severe performance penalties on larger tables.

Right.

Is the "estimated metadata" not compatible with the query test? In other words is this a bug or a limitation that cannot be overcome? If the latter, the test button should probably be unavailable if the estimated metadata setting is turned on, perhaps with a tooltip that says as much if you hover over the grayed-out button in the GUI.

There currently isn't a way for the provider to report that it is in capabable to deliver the right count in that mode - so that GUI cannot adapt.

But the option isn't default (for the reason, that it produces unreliable results in cases like this) and the documentation points that out (context help: This can drastically speed up operations on large datasets, but may result in incorrect characterization of layers (eg. the feature count of filtered layers will not be accurately determined).)