Juniper EX3300 "Storage size changed"

In the last three weeks I've started getting the following messages on two EX3300 stacks:

/dev/md18, mounted on: /var/rundb Storage size changed: 0B -> 117MB (/dev/md18, mounted on: /var/rundb)
/dev/da0s3d, mounted on: /var/tmp Storage size changed: 0B -> 368MB (/dev/da0s3d, mounted on: /var/tmp)
/dev/da0s4d, mounted on: /config Storage size changed: 0B -> 61.7MB (/dev/da0s4d, mounted on: /config)
/dev/da0s2a, mounted on: / Storage size changed: 0B -> 183MB (/dev/da0s2a, mounted on: /)
/dev/da0s2a, mounted on: / Storage size changed: 0B -> 183MB (/dev/da0s2a, mounted on: /)

Each stacks is made up of seven switches running version 12.3R12-S10. My google-fu has failed me in finding a resolution. Has anyone else seen this before?