Belgian Stamps On 1935 Hawaii Cover

Granted, Hawaii was still a territory in 1935 but ... wouldn't this be considered illegal usage?

I call shenanigans.

UPU rules for paquebot mail say that if on the high seas, the stamps of the country of the ship's registration are used. If in port, then the stamps of that country are used; however, mail is often found with stamps of last port of call often enough (strictly not by UPU rules). Paquebot mail can be cancelled in transit or upon landing.

Matson line ships were US-registered ships at the time and only went between the US mainland and Hawaii. There is no justification for using Belgian stamps. Worst of all, these are World War I era stamps, the left one invalidated in 1931 and the other in 1915.

Paquebot covers can be weird but this one is an impossibility. Nice Eleele cancel, though.