/proc/vz/vestat and /proc/stat (inside container) sometimes reports bad value for idle and wait

I'm trying to write a perl collectd plugin to track resource usage for openvz containers. The host is Debian lenny running kernel 2.6.26-2-openvz-amd64 on an Atom 230 processor. The guest is also Debian lenny amd64. Every once in a while, when running 'vzctl <veid> exec cat /proc/stat', the value for idle on cpu0 will be 48485, wait will have a value somewhat lower than the previous (10 seconds prior) reading for cpu0 idle, and the remaining values in the line will all be 0. On the next reading, all values will be what I expect.

example:

veid: 101
  cpu-0: user: 34200 nice: 39258 system: 39269 idle: 33410749 wait: 5961 interrupt: 0 softirq: 0 steal: 0
  cpu-1: user: 23359 nice: 12880 system: 21009 idle: 129 wait: 0 interrupt: 0 softirq: 0 steal: 0
veid: 101
  cpu-0: user: 34200 nice: 39259 system: 39270 idle: 48485 wait: 33369476 interrupt: 0 softirq: 0 steal: 0
  cpu-1: user: 23359 nice: 12880 system: 21012 idle: 129 wait: 0 interrupt: 0 softirq: 0 steal: 0
veid: 101
  cpu-0: user: 34201 nice: 39260 system: 39274 idle: 33413248 wait: 5961 interrupt: 0 softirq: 0 steal: 0
  cpu-1: user: 23412 nice: 12881 system: 21022 idle: 129 wait: 0 interrupt: 0 softirq: 0 steal: 0