This has been happening and I don't think it is only in low profile leagues, it does happen with big leagues. I recall there was a time it happened years back in Scottish premier league involving rangers, can't remember the other time now. When it was realized, it was immediately pulled down because rangers got a higher odd against lower team. Rangers later won the match as expected and it was big cash out for those who took the opportunity.

It is true that it could have a very rampant occurrence in lower leagues because bookmarkers might make mistakes more there than they would with popular top leagues.