as far as I can tell, this should work. A simple test:
test1.sah:
_log("ok");
test2.sah:
if (true) {
_include("test1.sah");
}
When I run this from the Sahi Controller, I get an "ok" logged. Maybe recreate this test and check if you get the same results. Maybe it's the ";" missing after your includes? Are you passing dynamic values to include? like _include($path)?