It happens from time to time, but after few minutes when recalculation kicks off it comes to normal.

I have a suggestion for those who are impatient (and think they are loosing shares) - add startum, stratum2, atratum3 and api to your miner and use 'load balance' as strategy. This way even if there is a problem with one of the hosts and/or shares are lost (though i doubt so - it just takes time for them to appear), then you will still get all shares from the rest of the backends. In case of connection issues with some of them you will still submit shares to the rest.