Great bug into php3_merge_dir()

I really cannot understand the logic used into the php3_merge_dir() function of mod_php3.c! According to me it's bugged!!! Let's make an example. I want to make php disabled by default and then enable it only in some selected directory of some virtualhost. So I put a "php3_engine off" into the root of httpd.conf (outside of every virtual host). Then I put a "php3_engine on" into some <Directory xxx> into some virtualhost, so (I thought) php is enabled only there. Well, this configuration doesn't works because of the incomprensible php3_merge_dir() logic: it only add new commands into a new directory configuration only if they are different from the default configuration. That is, "php3_engine on" is NEVER added!!! Please, tell me if either I'm terribly stupid, or the php3_merge_dir() is terribly bugged! Thanks.