For other's interest, this patch wasn't applied to the OpenACS 4.6.3 I downloaded (I was running OpenACS 4.6.3 on PG 7.3.5).
Ola's patch was applied to version 1.25 but not 1.24.2.2, which is the 4.6.3 revision. See CVS.
This means that OpenACS 4.6.3 isn't fully PG 7.3 compliant. Maybe I should be upgrading to 5.0.4 to avoid other, similar problems with PG 7.3?