I switched to the latest master branch and it seems it works better, but unfortunately I can't understand how much PKG memory kamailio really uses to know it still has problems with PKG.
For instance "kamcmd pkg.stats" always shows that tcp_main process has free: 32627984 (started with -M 32), while real_used: 22560048 and RES in top output for the same process is 8904.