Counter of type RateOfCountsPerSecond32 always shows 0

Question

I have a windows service that serves messages of some virtual queue via a WCF service interface. I wanted to expose two performance counters -

1. The number of items on the queue
2. The number of items removed from the queue per second

The first one works fine, the second one always shows as 0 in PerfMon.exe, despite the RawValue appearing to be correct.

I'm creating the counters as such -

    internal const string PERF_COUNTERS_CATEGORY = "HRG.Test.GDSSimulator";
    internal const string PERF_COUNTER_ITEMSINQUEUE_COUNTER = "# Messages on queue";
    internal const string PERF_COUNTER_PNR_PER_SECOND_COUNTER = "# Messages read / sec";

if (!PerformanceCounterCategory.Exists(PERF_COUNTERS_CATEGORY))
{
    System.Diagnostics.Trace.WriteLine("Creating performance counter category: " + PERF_COUNTERS_CATEGORY);
    CounterCreationDataCollection counters = new CounterCreationDataCollection();

    CounterCreationData numberOfMessagesCounter = new CounterCreationData();
    numberOfMessagesCounter.CounterHelp = "This counter provides the number of messages exist in each simulated queue";
    numberOfMessagesCounter.CounterName = PERF_COUNTER_ITEMSINQUEUE_COUNTER;
    numberOfMessagesCounter.CounterType = PerformanceCounterType.NumberOfItems32;
    counters.Add(numberOfMessagesCounter);

    CounterCreationData messagesPerSecondCounter= new CounterCreationData();
    messagesPerSecondCounter.CounterHelp = "This counter provides the number of messages read from the queue per second";
    messagesPerSecondCounter.CounterName = PERF_COUNTER_PNR_PER_SECOND_COUNTER;
    messagesPerSecondCounter.CounterType = PerformanceCounterType.RateOfCountsPerSecond32;
    counters.Add(messagesPerSecondCounter);

    PerformanceCounterCategory.Create(PERF_COUNTERS_CATEGORY, "HRG Queue Simulator performance counters", PerformanceCounterCategoryType.MultiInstance,counters);
}

Then, on each service call, I increment the relevant counter, for the per/sec counter this currently looks like this -

messagesPerSecCounter = new PerformanceCounter();
messagesPerSecCounter.CategoryName = QueueSimulator.PERF_COUNTERS_CATEGORY;
messagesPerSecCounter.CounterName = QueueSimulator.PERF_COUNTER_PNR_PER_SECOND_COUNTER;
messagesPerSecCounter.MachineName = ".";
messagesPerSecCounter.InstanceName = this.ToString().ToLower();
messagesPerSecCounter.ReadOnly = false;

messagesPerSecCounter.Increment();

As mentioned - if I put a breakpoint after the call to increment I can see the RawValue constantly increasing, in consistence with the calls to the service (fairly frequently, more than once a second, I would think) But the performance counter itself stays on 0.

The performance counter providing the count of items on the 'queue', which is implemented in the same way (although I assign the RawValue, rather than call Increment) works just fine.

What am I missing?