[CentOS] memory cgroup max_usage_in_bytes question

hi all,

can someone help explaining what we are seeing? it makes no sense to us.
this is a host running centos 7.4 with 3.10.0-693.17.1 kernel, and it
has 192GB of ram

> [] free -b
>               total        used        free      shared  buff/cache   available
> Mem:    201402642432 14413479936 75642777600    48586752 111346384896 185689632768
> Swap:   21474832384    31961088 21442871296
> [] cat /sys/fs/cgroup/memory/memory.max_usage_in_bytes 
> 273102151680

how can the max be so much higher than total, and this is not even memsw?

either we're very tired and are overlooking something obvious, or
there's something new to be learned ;)

many thanks,

stijn