Can't run concurrent LoadLevel processes?

It appears that Unity completely locks up if I attempt to run LoadLevelAdditive on one scene while LoadLevelAsync is running on another. Is this a known issue? Are there any workarounds?

Here are some more details on the structure of my game for those who are interested:

This title has a menu with a gallery in the same scene, with the main game in a separate, complex scene. Here are the two things I'm attempting to accomplish:

1) The primary game scene is large, so at the start of the title/menu scene I run a coroutine running LoadLevelAsync on it to cut down on a noticeable loading time. I'm disabling allowSceneActivation when I begin this procedure so I can jump to the scene when the player is ready. This works alright on its own.

2) The game's gallery contains a large amount of assets that players won't typically be viewing. I thought I would pack these models into separate scene packs and load them in with LoadLevelAdditive. This also works alright on its own.

Thanks in advance.