The use of mixed (monopole-dipole) phasing of a set of ICRF antennas is potentially useful to optimize tokamak performance. However, recent mixed-phasing experiments on JET, described here, showed undesirable antenna-plasma interactions under certain circumstances. A possible physical mechanism to explain the experimental results is discussed, viz. parallel currents flowing between adjacent antennas with different phasings can lead to arcing on the antenna with the largest sheath voltage. Means of controlling the interaction are discussed.