Sitecore contacts error with FlushContactToXdb method

Working with contacts and custom data, during the identification process in some cases the FlushContactToXdb method on ContactManager was giving the following error:

An unhandled exception of type 'System.StackOverflowException' occurred in mscorlib.dll

As with many of the community I was using the ExtendedContactRepository class from Brian Pedersen. It turns out that there was a possibility for infinite loop with the GetOrCreateContact method, which is detailed here. Effectively the repository was attempting to save a contact as new when it already exists with the given identifier.

An update to the repository appears to solve the issue in my case.