Jarngreipr not functioning correctly when trying to upgrade a dex skill gem

While using Jarngreipr, I am able to learn new skills that my strength satisfies in place of dex.

Here's the bug: If I want to upgrade whirling slash I am unable to. See below pic, I currently have level 4 and would like to upgrade to level 6. I am able to learn new dex skills that I don't have yet, but unable to upgrade.

Bug still remains.