[plt-scheme] mzc's ++ldf flag

I have a problem with the ++ldf flag of mzc:
#v+
jpc at jpc ~/Projects/avr] mzc --exe avrp ++ldf "-framework IOKit -lusb"
avrp.scm
mzc version 360, Copyright (c) 2004-2006 PLT Scheme Inc.
  [output to "avrp"]
[jpc at jpc ~/Projects/avr] otool -L avrp

avrp:
         /Users/jpc/Desktop/PLT
Scheme/lib/PLT_MzScheme.framework/Versions/360/PLT_MzScheme
(compatibility version 0.0.0, current version 0.0.0)
         /usr/lib/libSystem.B.dylib (compatibility version 1.0.0,
current version 71.1.4)
#v-

So it seems to completely ignore this flag (I assume it should link to
libusb and IOKit). ++ldl usb doesn't work either. It seems mzc doesn't
call the linker at all because adding nonsense flags doesn't result in
any errors (kdump also doesn't show any execves).

The libusb is loaded by means of foreign.ss which fails to load IOKit
automaticaly so I tried to link it by hand in hope it will find the
symbols. Even if this is not the way to go mzc still behaves strangely.

-- 
Regards,
Jakub Piotr Cłapa