This paper chronicles some issues that arose in attempting to implement two simple planners that interleave planning and execution. (For brevity, such planners will be called IPE planners.) The IPE planners are based on UCPOP (Barrett et al. 1993), a classic operator-based planner using goal-regression. Unfortunately, while the planners succeeded on very simple problems, they failed on problems as easy as the Sussman problem. This paper describes the two IPE algorithms and discusses why they failed.