Naming multi-instance performance counters in .NET

Question

Most multiple instance performance counters in Windows seem to automatically(?) have a #n on the end if there's more than one instance with the same name.

For example: if, in Perfmon, you look under the Process category, you'll see:

...
dwm
explorer
explorer#1
...

I have two explorer.exe processes, so the second counter has #1 appended to its name.

When I attempt to do this in a .NET application:

• I can create the category, and register the instance (using the PerformanceCounterCategory.Create that takes a CounterCreationDataCollection).
• I can open the counter for write and write to it.

When I open the counter a second time (in another process), it opens the same counter. This means that I have two processes fighting over the counters.

The documentation for PerformanceCounter.InstanceName states that # is not allowed in the name.

So: how do I have multiple-instance performance counters that are actually multiple instance? And where the second (and subsequent) instances get #n appended to the name?

That is: I know that I can put the process ID (e.g.) on the instance name. This works, but has the unfortunate side effect that restarting the process results in a new PID, and Perfmon continues monitoring the old counter.

Update:

I'm creating the category (and counter) as follows:

const string categoryName = "Test App";
const string counterName = "Number of kittens";
string instanceName =
    Path.GetFileNameWithoutExtension(
        Process.GetCurrentProcess().MainModule.FileName);

if (!PerformanceCounterCategory.Exists(categoryName))
{
    var counterCreationDataCollection = new CounterCreationDataCollection
        {
            new CounterCreationData(counterName, "",
                PerformanceCounterType.NumberOfItems32)
        };

    PerformanceCounterCategory.Create(categoryName, "",
        PerformanceCounterCategoryType.MultiInstance,
        counterCreationDataCollection);
}

I'm opening the counter as follows:

PerformanceCounter counter = new PerformanceCounter(
        categoryName, counterName, instanceName, readOnly: false);