Does this work correctly without purchasing? Does it kick in the following turn, or not at all?
Log might be useful to see if it's not reading the instant yield effect at all or glitching on it.
It's supposed to be fixed in the beta version (2.6/1.4), but as far as I can tell from my backup copy, it's the same as in 1.134/2.52, which means it should work there too correctly.