Call Fn.5 return value not consistent

[steve6375]

Issue seems to be that Fn.5 sometimes returns true and sometimes false!

call Fn.5 0 9 || echo YES

this works in mode 3 but not in 800x600 (it returns true and YES is not printed)

tested under VBox and QEMU - both show issue.

Is this a bug or can the result of a Fn. call not be relied upon?

[yaya2007]

BIOS: Console mode always returns 0. （Int 10/02）
BIOS: Graphics mode returns coordinates.

UEFI: returns coordinates.