The DE-like event in the plasma tail of comet C/2006 M4 (SWAN) which occurred on 27 October 2006 is investigated. Some phenomena in the comet’s plasma tail which appeared after the outburst of the comet brightness on 24.04 October are described. Typical sizes for the tail structure details evolving in consequence of plasma instabilities are determined. The velocity and acceleration of the disconnected fragment of the comet’s tail as well as the time of the event beginning are found. The DE-like event was likely caused by an encounter of the comet with a high-speed stream of solar wind.