Zr90 offers a very good case for the study of T=1 levels in the p1/2-g9/2 subshells and has recently been explored by several authros. Here earlier calculations of Thankappan and Waghmare are extended and analysed in detail. It is found that a simple central two-body interaction can be constructed which will give correctly the energy levels of the (g9/2)2 configuration, and hence also the levels of a (g9/2)n configuration. However, the same interaction fails to give correctly the levels of the other configurations (p1/2)(g9/2) and (p1/2)2. This simple two-body nuclear interaction is thus shown to be configuration dependent. It is pointed out that experimental identification of the as yet unobserved 4- level would be very helpful for further elucidation of this phenomenon. The results are compared with those of the other authors.