Higher magic and all its fun

[DGDobrev]

This means you can use the spellbook 4 times twice per round provided the first spell is 15 mana or less. When you use it 2 times in a turn, it will start showing 3/4. The second time you do so will result in 2/4, the third time in 1/4. This is the counter that shows how many times you can use the book twice per battle.

There is also a grey line that lets you know how many casts do you have in the current round.

There has been no bug regarding higher magic, and I, for one, never had such a problem and I do play Mage a lot, so you most likely used the spellbook 3 times twice per turn in this battle already.