vsz_limit of service doveadm "ignored"?

[Philipp]

Hello,

dovecot 2.2.18 on CentOS6.5

Jul 08 11:53:44 dsync-server(system): Fatal: master: service(doveadm): 
child 32554 returned error 83 (Out of memory (service doveadm { 
vsz_limit=521 MB }, you may need to increase it) - set CORE_OUTOFMEM=1 
environment to get core dump)

I tried increasing to 1 G, 1024 M or even disabling via value of zero -- 
to no change.

Every other service has the famous 18446744073709551615 B limit.
default_vsz_limit = 2 G

The second node with the same setup/config is happily accepting a higher 
value, since both
come from the same provisioning I cannot see (or expect) differences 
around ulimit and thelike.

The configuration comes from a single file, so no include drama or such.

Any pointers why the setting is being ignored?