What is the ruling on an Imam lengthening the second rak'ah more than the first?

Chapter on the Description of Prayer

Al-Mughni

Book of Prayer

Book 3 · Issue 2 · Bab 5

Open in Qurani

Primary text

If an Imam lengthens the second rak'ah more than the first, it is said to him, 'In this, there is learning' (meaning he should be taught otherwise).