Last most recent flight... busy day, lots of training flights entering the frequency area... One aircraft calling rolling 05 departing, visual of departing aircraft confirmed; frequent airfield op's of individual departing aircraft; flying neighbourly.
Call "xyz joining downwind 23 full stop"; field and area visual, clear.
Foreign aircraft responds; "entering back tracking 05".
Flying downwind, visual the field, no aircraft sighted entering and backtracking 05... respond "xyz to xyz, confirm last transmitted position"... no response...
Situational awareness raised to alert level... no aircraft sighted at transmitted position... continue flying downwind leg for 23.
Late downwind, foreign aircraft transmits, "backtracking 05"... visual field again, no aircraft sighted; look for possible powered parachute on field, no aircraft visual at transmitted position...
Situational awareness raised to High Alert, visual circuit airspace, no aircraft sighted.
Call "xyz base 23 full stop" status high alert... "xyz to xyz, please confirm present position", still no response... Extreme alert, prepared to bank hard right full power if required.
Call "xyz final 23 full stop"... "foreign aircraft responds "xyz to xyz, we will hold to the side of 05 for you"... "xyz to xyz, thank you appreciated"... still no visual of foreign aircraft at transmitted position.
Call "xyz late final 23 full stop", then spot foreign aircraft, cessna semonile twin, 50 metres off port side 11 o'clock at 500' AGL flying dead side of 05... (i.e 50 metres off port side flying opposite direction at same altitude while on late final for 23). WTF????
Requested debrief from command pilot of departing aircraft for confirmation of event... not an isolated event situation.
Shared the story with club CFI... Club CFI personally contacts owner/instructor of seminole for incident discussion...
Seminole owner/instructor response "he (me) never made any calls".
CFI's response, "that's impossible".
Seminole "why?"
CFI's response "because he's (me) anal retentive, and he always makes calls"...
Somebody screwed up, and it wasn't me...
Somebody will eventually die.. hopefully it won't involve me...
Nothing further to add...