What’s new in 3.19:
*) fixed problem - web proxy used up all router memory
if unlimited ram caching was enabled;
Install v3.20/or the lastest/ and try again 
Also have a look at this: http://forum.mikrotik.com/t/interface-stats-and-cpu-usage-not-correct-after-upgrade/24752/24
Hey keep us informed of the issue and the solution 