Channel aware schedulers of modern wireless networks - such as the popular Proportional Fairness Scheduler (PFS) - improve throughput performance by exploiting channel fluctuations while maintaining fairness among the users. In order to simplify the analysis, PFS was introduced and vastly investigated in a model where frame losses do not occur, which is of course not the case in practical wireless networks. Recent studies focused on the efficiency of various implementations of PFS in a realistic model where frame losses can occur. In this work we show that the common straight forward adaptation of PFS to frame losses exposes the system to a malicious attack (which can alternatively be caused by malfunctioning user equipment) that can drastically degrade the performance of innocent users. We analyze the factors behind the vulnerability of the system and propose a modification of PFS designed for the frame loss model which is resilient to such malicious attack while maintaining the fairness properties of original PFS.