please raise a bug at https://bugs.adobe.com/jira/browse/FM and provide the stream example, the code you're using to load the player that you are using (if it's not standard) and some other details that could help me replicate your case.
The bug report is here.
Embed is standard using iframe and example code given with strobe download.
Please let me know if there is any further information I can report to help resolve the issue.
I replicated your problem using the data from the bug report.
On Firefox I get an answer from the server that's 9.7 kB long instead of 3.3MB.
I suspect either an asset problem or a strange behavior form Flash Player.
Before I forward the bug to the Flash Player team, can you verify that the issue appears with another asset on the same server? Maybe you could change the encoding parameters?
A different asset is being used with SMP here:
By encoding do you mean the encoding of the video file or are ther some encoding parameters I should supply to the player?