Terminal "split pane" option appears to be broken

When using Terminal, if I select View--> Split Pane or use the keyboard shortcut (Command+D), rather than splitting the pane, Terminal removes the window background. I'm left with a nonfunctional, "clear" window. It doesn't re-draw window content until the window is resized, and at no point does it actually split the pane. Tabbed windows work fine, split panes absolutely appear to be broken. First screenshot shows a small window (superimposed over this post!) - second screenshot shows results of Command+D. Note that only the window border remains visible. Everything you see "inside" the Terminal window in second screenshot is actually the macOS Discussions post in the web browser window below the Terminal window. Is this a known bug? It seems pretty big not to have been noticed before.