From a cursory glance at SCI16's opcodes.s and SCI32's optbl.i, then comparing that to SCI Companion, it's nothing about the set of opcodes. 0x7D and 0x7E are bad-ops in one, but tracing tools in the other (filename and line number so the internal debugger can load the original line from source). Both are accounted for in SCI Companion, though it probably doesn't make any trace opcodes so successfully recompiling an SCI32 game may cause those to disappear.
It's also not likely anything with kernel calls, since those work the same as they always have.
Tangent: the SCI32 debugger would show the current source line in a window along the top of the screen. Whenever the file or line changed, it'd search for the source file, then display the nth line. Practical example?
SQInvItem::highlight:
_line_ 36 ;--> (method (highlight param1), you'd think, but I'm not sure...
_file_ "sqinv.sc" ;...because *here* it changes the file name...
_line_ 40 ;--> (= cel (* 1 (if argc param1 else 0)))
push1 ;...so that's either not the (method) form *or* there's a couple lines of docs.
lap param[$0]
bnt code_05dd
lap param[$1]
code_05dd: mul
aTop cel
_line_ 41 ;--> "(UpdateScreenItem self)"
push1
pushSelf
callk UpdateScreenItem, $2
_line_ 42 ;--> ")"
ret