CURRENT: memory leak?

I realise an exorbitant memory usage of FreeBSD CURRENT ( FreeBSD 12.0-CURRENT #16
r303470: Fri Jul 29 05:58:42 CEST 2016 ). Swap space gets eaten up while building
world/kernel and/or ports very quickly.

I see this phenomenon on different CURRENT systems with different RAM (but all ZFS!). No
box is less than 8 GB RAM: one 8GB, another 16, two 32 GB. An older XEON Core2Duo server
with postgresql 9.5/postgis acting on some OSM data etas up all of its 32 GB and
additional 48GB swap - never seen before with 11-CURRENT.

I didn't investigate the problem so far since I realized this memory hunger of 12-CURRENT
just today on several boxes compiling world, eating up all the memory, staring swapping
and never relax even after hours from the swapped memory.

Is this a known phenomenon or am I seeing something mystique?

Regards,

Oliver