Fully compliant bistable micromechanisms (FCBMs) have potential use in numerous applications, including switches, relays, shutters, and low-power sensing arrays. Two-dimensional finite element models for these FCBMs have been used in device analysis and design, and provided an adequate match to preliminary experimental data. However, with more extensive experimentation over a large range of designs, some results proved to be radically different than predicted, with trends not consistent with effects such as stiction or electrostatic forces. Two different types of behavior, Behavior 1 and Behavior 2, are observed and explained, only one of which is predicted by 2-D models. This paper tests the hypothesis that three-dimensional effects can dramatically influence the motion characteristics of FCBMs. Three-dimensional finite element models were constructed, compared to 2-D models, and validated for the purpose of testing the hypothesis. Off-axis and eccentric loads are shown to cause behavior consistent with experimental data for Behavior 2.