VBETEST crash when /M[x] key is used

[wbcbz7]

first issue :)

When using /M[x] key (override memory size), where x is NOT equal actual memory size in 64kb units, VBETEST.EXE from SciTech Display Doctor is unable to finish videomode test. While attempting to scroll virtual screen it crashes with this message:

CauseWay DOS Extender v3.25 Copyright 1992-96 Michael Devore.
All rights reserved.

Exception: 0E, Error code: 0006

EAX=00000000 EBX=00000000 ECX=0007FC00 EDX=00000000 ESI=004640AC
EDI=FF600000 EBP=00463F58 ESP=00463F48 EIP=0043D1AB EFL=00213214

CS=01A7-FFBCA000 DS=01AF-FFBCA000 ES=01AF-FFBCA000
FS=0000-xxxxxxxx GS=01B7-xxxxxxxx SS=01AF-FFBCA000

CR0=00000000 CR2=00000000 CR3=00000000 TR=0000

Info flags=00008042

Writing CW.ERR file....

CauseWay error 09 : Unrecoverable exception. Program terminated.

I think it crashes because VESA function 0x4F06 returns incorrect number of available scan lines in DX register, so we need to patch or rewrite this function.

p.s. freaking DOS extenders :)