I went back to the circuit and checked that the voltage at the LEDA pin is constant, and it sources a DC 1A regardless of the input level. This is without the switch.
When I add the switch and increase the frequency to 10 kHz or so, the current from the LEDA pin drops, which I am measuring with an ammeter, and the current through the LEDs are mostly DC currents where they should be AC since I'm switching the current between the two.
I am doublechecking the validity of the ammeter measurements by looking at voltage across the photodiode, which should be a pulse when the LEDs are switching properly. The photodiode has a DC current through it at higher frequencies.