Last thing I would try (maybe you did already) is connect to the HDMI (DVI) input and manually rename the port to PC (as described under “Editing external devices”).
Yes, I also tried this and nothing changed. Unfortunately this option is just for ease identification of the ports, nothing related with resolution or aspect.
Detects input as interlaced, that really very weird…
Indeed … Now I am just putting my hopes on the new lineX features on future OSSC firmware update. Maybe this can solve the incompatibility.