crafting tab isn't staying open

Hello @Dr.Kahl, welcome to the forums. Can you confirm that this is not a hardware issue? Cause if it is then your mouse is probably incorrectly signaling two clicks when you only press it once. Clicking twice on the crafting tab will open and then close it.To find out if it is a hardware issue, if possible find/borrow a mouse from someone else and see whether the issue still occurs.

If you somehow don't have an extra mouse on hand then you can instead utilize the "Open Crafting" Action from the Controls Settings in the Options menu. It is set to the "Tab" button by default but you can designate it to any other key instead. 

Opening the Crafting menu this way however requires you to be standing still cause the WASD keys will direct the crafting tab to which ever you wish to craft and pressing SPACE / ENTER to begin crafting the selected item.

I hope that helps, cheers.