logic is as follows
Heighten spell is unique among metamagics in that it actually increases the spell's level - not only the slot.
Thus, a heighten(x1) magic missile is a second level spell.
Versatile spellcaster can give you a slot a level higher than that listed on your progression, but normally you don't have any spells to put in that shot, and any other metamagic leaves it as a first level spell in a second level slot, et cetera. heighten actually increases the level, so since you're able to cast heightened cause fear, or heightened ILW, or heightened detect undead, you can cast second level spells. They're crappy second level spells, but they're still second level.