We recently switched to OpenBD on a production website and it uses MySQL FOUND_ROWS(). There a couple of things to ensure it works properly on OpenBD.
You need to add this setting to the "Connection Settings" in the datasource
The queries need to be in a cftransaction block otherwise they will use a different MySQL connection. It would look something like:
<cfquery name="foo" datasource="foo">
SELECT SQL_CALC_FOUND_ROWS * FROM foo
WHERE id > 2 LIMIT 2
<cfquery name="bar" datasource="foo">
SELECT FOUND_ROWS() AS numRows