darkSpyro

I have been replaying Skylanders, starting with this one. But when I decided to get all the hidden treasure chests, using the item, on every single stage, I came across Arkeyan Armory. The green circle never showed up, and I had already give up, when I saw this falling from the sky.
Do I need to shoot it?? Come closer? Or is it a bug, since sometimes it doesn't appear at all, or appears on the left side, near the rocks. Does anyone have a clue about it? (Sorry for the image quality)

I tought it was a bug, but I tried on another save file and the first time I entered the level with the chest, the circle never blinked, and after some retries I found it on the same place, while riding the robot. The Hidden chest doesn't work on Heroic Challenges (PS3 version at least

Ah, alright.
I was afraid that would be the case.
It never blinked because the chest icon disappears while on the giant robot, even though I can see it descending from the ceiling. (If I remove the chest from the portal, it disappears midway)
Thanks so much for the replies! Seriously? I always though that the Ps and Xbox versions were better than the Wii one. I remember I picked some chests before on this level, but this one is reallyyy bad placed.
Dolphin seems like a lot of work, but there's nothing I can do if those chests are behind a bug. (I would love a remaster, specially, of this one). That's another thing I didn't know, it's a shame it never got the english version.