Message cache conflict on block wise transfers with many chunks

[palsivertsen]

I get the following error message from the UDP client(?) when making a GET request with a large number of block wise chunks:

udp: handleReceivedMessage(Code: Code(136), Token: 8a0aa320cceb6969, Type: Confirmable, MessageID: 50032): cannot add message (Code: Content, Token: 8a0aa320cceb6969, ContentFormat: text/plain; charset=utf-8) to sending message cache: message(Code: Content, Token: 8a0aa320cceb6969, ContentFormat: text/plain; charset=utf-8) with token(8a0aa320cceb6969) already exist

I did a packet capture and it seems the client issues a 4.08 Request Entity Incomplete (136) response (instead of the next block request) when this error happens:

Commit 9fd9042 adds a test highlighting this issue.