Black taskbar-sized strip at top of screen

This probably isn’t OpenGL specific, but I’m running an OpenGL context inside of an MFC application on Windows, and whenever I maximize it there’s a black strip at the top of the screen, 62 pixels high. (Black is my clear color.) The CWnd::OnSize callback is getting passed a height of 988 where my screen height is 1050. I’d understand if it accounted for the taskbar, which is still visible at the bottom of the screen, but the black strip is at the top of the screen. I’ve tried a number of shenanigans, including auto-hiding the taskbar (no change), moving the taskbar to a different side of the screen (no change), hardcoding my screen’s height for my glViewport call (no change). Occasionally I get the black strip to be split between the top and bottom of the screen, however.

I’m even responding to WM_GETMINMAXINFO and providing the dimensions of the screen, and my OnSize callback is still getting a size of (1680, 988) instead of (1680, 1050). Even that seems to be academic, because, as I said, I’ve tried sending (1680, 1050) to glViewport with no noticeable change.