lmb-djaquier

### Prerequisites - [X] I have written a descriptive issue title - [X] I have searched [issues](https://github.com/cake-build/cake/issues) to ensure it has not already been reported ### Cake runner Cake Frosting...

Hello, I found incorrect Flurl behavior when re-using a Flurlrequest object with multiple PostMultipartAsyncs. For example, with this kind of snippet, to fetch some attachments from a famous support case...