Every ******* time. No matter where you send them or how many times you press the stop command. Grenadiers charge forward like nerds roleplaying as infernos and die horribly to the horrors of reality. You can bypass their stupidity by setting their move command to hold position, but It'd be nice if you didn't have to micro artillery that way.
This didn't happen before but was implemented with when titans came out and grenadiers changed from best to useless.