I have not come across this particular way of distorting FTF statistics so far, but as a CO I would certainly ask the person to change the log in a way that is not picked up by PGC for the FTF statistics (i.e. without brackets etc.).
However, I assume that this is a marginal phenomenon which does not really have a significant influence on FTF statistics.
There is, however, a different issue that has rendered them basically meaningless these last years. I do not know whether this is a widespread practice in other parts of the world, but here in Belgium it has become current practice (in some parts of the country) that organisers of events grant to all participants the opportunity to log an FTF on all caches of the event. As you can image this means that dozens of people log an FTF on dozens or more caches which they might have seen during the event (in the best case) or not. Contrary to the issue mentioned by you, which is limited to mala fide persons who deliberately want to cheat, these mass FTFs at events have created irritation in (parts of) the FTF community, but most of the people tag their finds at events as FTF without any bad conciousness, as the organisers of the event have allowed them to do so. The result, however, is evident: because of all these fake FTFs, FTF statistics have become meaningless and rather show now who regularly participates in events than those who still find pleasure in the good old FTF hunt, thereby spoiling the fun for the latter.
I had encouraged to implement a technical solution to this (cf: https://project-gc.com/qa/?qa=15272/any-possibility-to-exclude-mass-ftfs-from-statistics&show=15272#q15272),
but this discussion has, unfortunately, petered out and has not lead to anyhting.