This is not a bug, simply a feature request.

Would it be possible to add a scaling option to the inventory screen?
My suggestion would be holding [CTRL] and using the mousewheel, like with most browser windows.

This would both help people with bigger screens make the items look smaller (therefore getting more of the inventory on screen) and those on smaller screens (or with eyesight issues) able to make the icons bigger.

Another option would be a scaling slider in Options.