Do you use the FreeMiNT serial xdd drivers (scc.xdd, mfp.xdd, ...)?
yes and no :) on falcon freemint + scc.xdd but on megaste sting + hsmodem (drvin.prg, scc.prg, mfp.prg). maybe this is the reason but as far as i know, hsmodem should be as good as scc.xdd at least?