Future 5G networks will serve a variety of applications that will coexist on the same spectral band and geographical area, in an uncoordinated and asynchronous manner. It is widely accepted that using cyclic prefix-orthogonal frequency division multiplexing (CP-OFDM), the waveform used by most current communication systems, will make it difficult to achieve this paradigm. Especially, CP-OFDM is not adapted for spectral coexistence because of its poor spectral localization. Therefore, it has been widely suggested to use filter bank based multi carrier (FB-MC) waveforms with enhanced spectral localization to replace CP-OFDM. Especially, FB-MC waveforms are expected to facilitate coexistence with legacy CP-OFDM based systems. However, this idea is based on the observation of the PSD of FB-MC waveforms only. In this paper, we demonstrate that this approach is flawed and show that interference between FB-MC and CP-OFDM systems should be rated on precise estimation of the error vector magnitude (EVM). Our analysis, which is confirmed through simulations on both flat and frequency selective channels and software radio implementation, shows that the interference caused by FB-MC waveforms on CP-OFDM receivers is multiple orders of magnitude higher than expected in the literature. Finally, our results show that using FB-MC waveforms does not facilitate coexistence with CP-OFDM based systems to a high extent.