GROMACS

I'm getting a grompp error when I try to use the couple-lambda0
option in conjunction with vsites:
Source code file: /home/kasson/gromacs-4.5/src/kernel/vsite_parm.c, line: 392

Fatal error:
calc_vsite3_param not implemented for the general case (atom 3)
For more information and tips for troubleshooting, please check the GROMACS
website at http://www.gromacs.org/Documentation/Errors

I think it's coming in toppush.c when we do:

static void decouple_atoms(t_atoms *atoms,int atomtype_decouple,
int couple_lam0,int couple_lam1) {
int i;

for(i=0; i<atoms->nr; i++) {
   if (couple_lam0  ecouplamNONE || couple_lam0  ecouplamVDW) {
     atoms->atom[i].q     = 0.0;
   }
   if (couple_lam0  ecouplamNONE || couple_lam0  ecouplamQ) {
     atoms->atom[i].type  = atomtype_decouple;
   }
   if (couple_lam1  ecouplamNONE || couple_lam1  ecouplamVDW) {
     atoms->atom[i].qB    = 0.0;
   }
   if (couple_lam1  ecouplamNONE || couple_lam1  ecouplamQ) {
     atoms->atom[i].typeB = atomtype_decouple;
   }
 }
}

I tried checking for ptype == eptVSite, but I'm not sure that's set yet.

1. can you think of a better way to fix this?
2. is there some other indicator of a virtual site that's set by
this point in the code?

BTW I'm not trying to do quantitative free energy calculations with
virtual sites