i bet its totally because of the oms version.
or perhaps its to do with the MT4 interfaces OMS driver..
http://web.archive.org/web/20020603152527/http://www.emagic-mirror.com/pub/drivers/u8omsdrv.sit
it may have some differences between the way it works and the older interfaces that would have been used at the time
of vision 1.4. remember thats emagic writing a driver for opcodes OMS..  presumably primarily for use with logic + the mt4
+ oms.. not vision!!

kzb; if u could share some photos of your mac classic running vision 1.4 for educational purposes that would be really cool