Game within a game not launching properly

[BenjiBearPup]

In Tales of Phantasia Narikiri Dungeon X you can access Tales of Phantasia Full Voice Edition for PSP from the title screen via an icon.
When I click it using Managunz the screen goes black for a second and loads back to the title screen of Tales of Phantasia Narikiri Dungeon X instead of Tales of Phantasia FVE.
I have the same iso installed on my PSP and it works just fine there.
I'm not sure if it's a problem with a UMD containing multiple games or not but any help would be appreciated :)