The results of single-particle orbit calculations for the Wisconsin RF-heated tandem mirror experiment, PHAEDRUS, are presented. The plug ions confined near the central region are well-behaved in the sense that they drift favourably in the azimuthal direction and have circular drift surfaces. However, ions that have penetrated deeply into the magnetic well oscillate radially and drift unfavourably in the azimuthal direction. If the magnetic-flux tubes of the end plugs are oriented facing each other, central-cell ions confined electrostatically but penetrating deeply into the magnetic well can have large radial excursion and their drift surfaces are elliptical. This can be remedied by orienting the plugs orthogonal to one another. Ions confined near the central region have circular drift surfaces but in general drift unfavourably in the azimuthal direction. This unfavourable azimuthal drift can be the cause for microinstabilities while the radial drift can cause the ions to be lost from the system.