Triggering a trigger volume with a Capsule parented to a camera

On Answer Hub there is a question today about triggering an event using an object attached to a camera. The idea (if I understand right) is that an object is attached to a camera, and when the camera moves at some point the object enters a trigger volume and the event fires. Trying this myself with a Capsule held out in front of a camera, I’ve notice something odd. There is clearly something I don’t understand about how collision detection / triggering works and I’m hoping someone out there can explain it to me.


Basic 3rd person starter content.
An additional capsule parented to the FollowCamera and positioned way out in front. (See image)
A trigger volume is added to the scene. The idea is that when the camera moves, the extra capsule parented to the camera enters/leaves the trigger volume and causes some text to change color.


At first I thought this was working as I expected, but I’ve noticed something strange. If the character is moving forwards/backwards, the text changes colour appropriately whenever the additional capsule enters/leaves the trigger volume. However, if the character is standing still, moving the mouse rotates the camera and moves the capsule parented to the camera in/out of the trigger volume (I can see the capsule moving), but nothing gets triggered. No event gets triggered until I press forwards/backwards on the keyboard; as soon as I press the move forward/backward key the color updates dependent on the current position of the capsule relative to the trigger volume (i.e. whether the capsule is in/out of the trigger volume when the button is pressed, not whether pressing the button moves the capsule into the trigger volume).

In short - it seems that it is not just whether a capsule enters/leaves a trigger volume that matters as far as triggering is concerned. Some kind of additional input seems to be needed to get the engine to check whether collision is occurring between a capsule and a trigger volume. Can anyone explain what is happening?