I have a Lenovo ThinkPad Yoga running WIN 8.1. Its screen resolution is set to the recommended size of 1440 x 900.
The laptop is connected to a second monitor (Acer V196WL) that is set as the main display. Its screen resolution is set to the recommended 1920 x 900. This set-up worked fine until a few days ago after I connected the laptop to a projector. Since then, the icons and text are extremely small on the laptop and so-so small, but workable, on the external monitor.
I have the "make text and other items bigger" setting at medium (recommended). The "let me choose one scaling level" text box is unchecked.
It appears that the medium setting is actually displaying at small. When I bump it up to large, it displays as if it is set to medium.
An EE member suggested that I change the laptop to main display, which I did, and I thought that this resolved the issue (so I closed the question). However, when I switched back to using the external monitor as the main display, the problem reappeared. So, the additional data point is that the secondary display renders incorrectly, but the main display renders correctly.