Model networks were prepared by the reaction of monodisperse polybutadiene, containing 8% of double bonds in the 1,2 vinyl position, with p-bis(dimethyl silyl) benzene at different stoichiometric imbalances. Small strain modulus and measurements of the gel fraction indicate important differences with the predictions from ideal network forming reactions and the molecular theories of rubberlike elasticity. Sol extractions are higher than expected and small strain moduli are consistently low. Other macroscopic signs of the departure from ideal behaviour are detected. The onset of the gel point is delayed to a degree that grows with increasing imbalance of the reactive groups. We consider all the possible explanations for the observed behaviour, and suggest that the most likely one is the presence of intramolecular reaction. We also propose a simple theoretical model to confirm that our assumptions are consistent with the experimental results.