Lego Mindstorms Robots are a popular platform for graduate level researches and college education purposes. As a portation of nxtOSEK, an OSEK standard compatible real-time operation system, EV3OSEK inherits the advantages of nxtOSEK for experiments on EV3, the latest generation of Mindstorms robots. Unfortunately, the current version of EV3OSEK still has some serious errors. In this work we address task preemption, a common feature desired in every RTOS. We reveal the errors in the current version and propose corresponding solutions for EV3OSEK that fix the errors in the IRQ-Handler and the task dispatching properly, thus enabling real multi-tasking on EV3OSEK. Our verifications show that the current design flaws are solved. Along with this work, we suggest that researchers who performed experiments on nxtOSEK should carefully examine if the flaws presented in this paper affect their results.