Not totally unheard of. Cichlids will put eggs wherever they fancy the most, for whatever reason. We may not find it normal but that's prolly where they think is the best spot for eggs.
ive had convict cichlids do this in my 50 gal ina tank with a bunch of other africans it gave them an edge defending them from the either fish they could secure almost half of a 50gal
had fry kept 15 used the rest as feeders to my oscars