How to create multiple Mutagen of same type?

I have 9 'Lesser Blue Mutagens'. In Alchemy, I can create 1 'normal' Blue Mutagen with 3 of this small mutagens.

But if I try to make a second 'normal' Blue Mutagen, I get the hint: "You already have this item". Thats true, but I need 3 of the 'normal' Blue Mutagen for the next 'Bigger Blue Mutagen'.

What do I have to do to create multiple 'normal' or 'Bigger' Mutagen from 'Lesser' mutagens?

This is a bug introduced in path 1.05. You can work around it by dropping the crafted mutagen on the ground. Then you'll be able to craft another one. You'll have to repeat this until you have enough mutagens to craft the greater mutagen.

This bug is fixed in patch 1.06 that was released just now