Rating range resets seemingly at random

Hi, I like to play blitz with a somewhat narrow range. Say -50/+50. I leave this setting along and rarely touch it. Occasionally I'll sign on to play a session of live chess and click the "New 5 Minute" button on the homepage or some such method of entering into a new pairing. Most days it remembers and keeps my previous rating range selection, however on occasion I'll get into playing games and notice that I've been paired with a user outside of the 50 point range that I thought I had set sometimes 200 or more points! Once I notice this and go and check the setting on the Side Meny > Play > Play screen and open the custom accordion section. I see that it has reset somehow to -∞/+∞. 

So the question here is, why does it reset? Is there anything I can do to avoid this? Can I set a new default so that if it does reset it's not pairing me with people radically lower or higher than my current rating? 

Thanks.