Exception in handler sampling all metrics

[borithefirst]

I am using forkServer to monitor my app and getting the following error when querying the JSON of all metrics. "proxy.msgprocessed.41" is the name of one of the counters (message count for type 41).
I am a bit surprised, how can the handler of this request fail in this way? Does it somehow register metrics?

A web handler threw an exception. Details:
The name ""proxy.msgprocessed.41"" is already taken by a metric.
CallStack (from HasCallStack):
  error, called at ./System/Metrics.hs:214:5 in ekg-core-0.1.1.3-KlzBjumHCxCGGp8JdgUhg8:System.Metrics