I suggest you to run 3.7 version on both routers, then compare value.
In case there are any similar problems, contact MikroTik support [firstname.lastname@example.org
It's 100% bug. Not sure how many conntracks are supported , but the number really depend of amount of RAM.
In MT case it' s always (I have it starting from 3.3) "Max Entries: 524288" in case if RAM equal or more then 512 MB.
In real life 512MB = 524288KB, exactly what we have.
If we are talking about max contrack then it should be 65536 in case if you have 1Gb and something around 131072 in case of 2G RAM
Like example Linux with 1G Ram show:
ip_conntrack version 2.4 (8192 buckets, 65536 max)