We're all familiar with the wonderful LNF rate and its great savings potential (and if you're still not familiar than have a look in my guide here: https://www.rewards-insiders.marriott.com/message/165855#165855).
Marriott LNF team has recently decided to rule out a few websites from being used as a comparison source due to them not resulting in an actual reservation in the Marriott system after using them to book through.
These websites are (as for this moment and may change any time):
ostrovok.ru (and all its versions)
I have updated my guide accordingly.