I'm having some trouble getting this function to work correctly. 
My pdb is called junk and residue 94 is the c-terminus, and I want to add a tryptophan to it- here's my input

editor.attach_amino_acid('junk & resi 94 & name c', 'trp')

The result is that the tryptophan is built, but it's not bonded (it's a separate object, actually). Could anyone tell me what I'm doing wrong?  Thanks,