I've had it happen to me a couple of times now where I have a treasure token available to be able to cast a sorcery speed still in my first main phase after casting a spell, but the treasure is necessary to cast the spell at sorcery speed. However, immediately upon casting a spell that uses enough mana to require the use of a treasure token to cast a sorcery spell still in my hand, it jumps to combat without giving me the opportunity to cast the additional spell at sorcery speed.

This has happened on the pc steam client.