This topic is mentioned in the ISOCAM Observer's Manual, sections 2.1 and 4.7 . The behaviour of the instrument is unchanged, but the recommendations have been substantially strengthened:
Observers should avoid using the 12"/pixel lens if possible and should use the 6"/pixel lens instead. Because of the memory effects in LW, a few hundred frames following the 12"/pixel observation carry the imprint of the field stop. If you use the 12"/pixel lens, you MUST include a CLEAN at the end of your observation. This is necessary to minimise damage to the observations of the following observer.