We report that during focused ion beam chemical vapor deposition (FIB-CVD) the effect of deposition is not limited to the area where the ion beam scanning takes place but occurs on regions which are out of sight of the incident beam and extends up to several micrometers away from the specified site. This phenomenon has deleterious effects, especially when the nanocontacts are fabricated for the electrical characterization of the nanodevices. The deposition occurs into the gap between the contact pads and acts as a resistance in parallel with the resistance of the nanostructure to be measured. The extended deposition has been explained on the basis of molecular cracking of the precursor gas molecules induced by forward scattered Ga ions, and appropriate measures to remove the effect have been suggested.