IP address change during session

I have seen this several times with cookie persistence. One case was for management session, where LTM log reported: May 26 14:03:59 slot1/xxxxxxxxx err httpd[9206]: [error] [client x.x.x.x] AUTHCACHE Error processing cookie 2820043E925........944A550 - Cookie impersonation detected from remote IP x.x.x.x to remote IP y.y.y.y, referer: https://z.z.z.z/xui/modals/en/error.html?1401087541630

This was tracked to be an administrator removing his laptop from docking station while session, thus roaming from fixed to WLAN.