Seems related to the input language of the keyboard.
Dutch works fine, except of course some key combinations produce extended ASCII codes. English, the On-Screen Keyboard shows both Alt keys pressed. And seemingly Windows reports an ASCII or Unicode if the right Alt key is pressed. Will look into that.
The problem was caused by a fix for keyboards (like Nordic) that produce standard ASCII characters for some Right Alt key combinations.
vDos previously tested if Windows returns an Unicode that resolves to a supported extended ASCII character. If not, Alt+key was reported to DOS, else the extended ASCII character.
That of course didn’t work with those keyboards returning standard ASCII characters. That was then fixed. Windows however returns an Unicode with US keyboards. Don’t know why it does so, but I excluded US keyboards from this testing procedure.
As said, the right Alt has some extra code to deal with specific circumstances where vDos should report a standard ASCII value instead of the Alt key combination. With the exception of the US keyboard now added.
I was unable to reproduce your issue with the left Alt by setting the keyboard layout to Greek - 220L.