Version: Android 1.1.1
I happened to complete a quest at the same time as getting a large amount of loot. After pressing A on an item to look at it in the item menu, dialogue for the next step of the quest appeared over the item screen, and I was forced to proceed through the entire interaction before being able to access the item menu.
This isn’t really a serious issue, but it might be less confusing to have all quest dialogues wait to appear until the player has closed all menus and is looking at the field. This would make it consistent with the behavior exhibited by your quest and achievement announcements, which currently wait to be shown until all menus are closed and the player is looking at the field.