Ist DtlsTransport thread save?

[ds600]

I have a library (COAP.NET) that uses bouncy castle. It uses the DtlsTransport.Receive Method to handle the DTLS part everytime a package arrives.

In its current implementation it always runs the receive method in a new Task.

With this implementation Bouncy Castles DtlsRecordLayer.ProcessRecord always throws a critical error on

if (decoded.len > buffer.Length)
                throw new TlsFatalAlert(AlertDescription.internal_error);

Because it tries to write larger content into a buffer sized for the previous (or maybe next) package. This only happens if the packages arrive at a somewhat fast interval and have different sizes.

User error in the COAP.NET library, or is something else going on here?