Dam the Man wrote:
I think it would get added to the stack of the active player's trigger tiles. Even though:
"When you advance the Event marker or the
marker on the main Activity line on your turn,
collect the trigger tiles that the marker passes
over and the one that it stops on and place them
facedown in front of you." (p. 4)
Agreed. In addition, from the Friends & Foes rulebook about Frodo's Determination:
"...Frodo may advance any one Activity marker by one space and carry out the space for himself"
I would argue that the Battlefield tiles, while connected to the spaces, are actually not part of the spaces, and so get resolved independantly as quoted from the Battlefields rules above.
Great question, and great job identifying it in the subject field!
Also, you may want to cross-post this topic on the Friends & Foes page, since it involves both.