Mystical Teachings showing to select same 2 spells instead of 2 differents

Keyler

The text of the spells says, Pick one of the first 2 different Spell cards...
Lot of times Mystical Teachings spell shows you the same spell to choose instead of 2 differents.
If you build your deck with only one spell (other than Teachings) sometimes the same spell is showed twice to choose (2 same cards) and other times only one (only one card).
When you build your deck with 2 or more spells (other than Teachings) sometimes you can choose between 2 different spells and other times 2 spells are the same.