I'm sure I had this problem ages ago. But normally I use Toxic on a real ST. I remember reading a thread recently that said there's no one using Monst when Steem Debug is so powerful..... well I still use Monst(Toxic) so there!!

Tip. Load makeboot into monst, trace through, you'll see a part saying sub #$18000  what this does is make toxic load at ramtop minus $18000 bytes (this happens when you press right shift on boot).  Try changing this to a higher value e.g. $80000 or something. Then execute makeboot.

Shw

If this doesn't work I'll investigate.