Factorio Forums

Normally middle mouse button is used to lock items on toolbar.
If you map it to enter/leave ar this function stops working and there is no way to remap it to different button curently.

GUI button interaction has to be mapped to a mouse button to function. The widgets (buttons) don't respond to any other input so the game doesn't know you're trying to interact with them.

Yep I managed to use one of additional mouse button for locking.