Short Approach?
From what you say it seems that the aircraft was not complying with an ATC instruction......and therefore carrying out an illegal manoeuvre. In an extreme case this practice could compromise not only the safety of the subject aircraft and its passengers, but also the safety of other airspace users.
Hopefully there will be sufficient evidence to absolve ATC of any liability should this practice continue.
TOP TIP: keep a record of these occurrences to set up a database......not necessarily a full blown official report.....the aim is to help everyone rather than cause upset.
PRECEDENT: aircraft given a surveillance radar approach [SRA]...traditionally the controller gives headings to maintain track....adjusting as necessary for wind change etc. The aircraft flies the assigned heading as instructed. Peculiar things started to occur when pilots just set the track required and the aircraft flew its own constantly/continuously corrected headings instead...and without the knowledge of the controller. In such cases the controller was then completely unable to give an SRA because his/her reference heading was no longer valid.