[j-nsp] jnxOperatingTemp issues on ex4500?

[Jonathan Call]

If I run 'show snmp mib walk jnxOperatingTemp'  on an ex4200-24t I get valid (i.e. non-zero) temperature readings for the FPCs and Routing Engines in it. If I run the same command on an ex4500-40f all of the entries return a non-operational status (i.e. zero). All of them are running 11.4R1.6.
Has anyone encountered something similar?
Jonathan