In one of the last 4 or 5 updates it was clearly stated the when you stable pets who are guarding oyu they will remain in guard mode. AND that players can only have 5 pets guarding them at any one time, SOooooo if oyu get on youe mare and have your beetle out and have them guard you = 2 stable them and get great = 3, stable and get your 2 drakes = 5, now go back and get your mare / ice wyrm , if you left all your previous pets guarding you your wyrm will never be able to go inot guard mode.
Simple fix pull out your pets and tell them all to STOP then stable this wil clear your guarding list.