SPIDEV1 / UART1 conflict?

I have an app running on several BBBs now, for which I needed both SPI and a UART. I was pleased to discover that the SPIDEV1 overlay, which conflicts with HDMI, does not seem to conflict with HDMIN, so I get a GUI as well. SPIDEV1 does not explicitly conflict with UART1 either, and they share no pins, but it is consistently repeatable behavior on all my BBBs that when I use SPIDEV1, UART1 does not behave correctly–sometimes sending works, but receiving does not. When I switched my app to use UART4 instead, all worked nicely.

So is there an undocumented conflict somewhere between SPIDEV1 and UART1, and should it be documented?