Before the “Heavy Cavalry” update, damaging the trailer only disabled the flamethrower. Now, after the trailer is destroyed, the entire tank (Churchill Crocodile) explodes.
You can bug report it here: Gaijin.net // Issues (just search a bit first so that you don’t report something that is already reported and known about)
A guide on how to report bugs can be found here: ([Navigation] Technical Knowledge Base | War Thunder Wiki)