CM5.2 using 8410D sets. Sets are in a pickup group and a coverage answer group. Call comes in to a station, if someone does not use the pickup button to answer the call the coverage path will route the call to the coverage answer group and everyone's phone will ring. This works with only one issue-their pickup button flashes for an unknown reason. Call pickup and enhanced call pickup alerting are turned off. We cannot recreate the pickup button flutter when we do test calls. Unsure what is causing this.