Simulate download causing Stream Errors

I have a movie that asks some question to a bunch of php files and load images based on the answers. Nothing too fancy in the connection, and it works well.

Problem is, as soon as I hit the “simulate download” button, I’m instantly flooded with “Stream Error” messages.

Two things are odd here:

  1. Stream errors should happen when the URL does not exists, but not only it does, it can be accessed when I do the regular movie testing.
  2. The instantly appearing message point out that the code is being executed, but it hasn’t been loaded yet! I’m talking about 70 kb of code being executed in the first second, while simulating a 56k connection.

Bug? “Simulate download” feature? Known pitfall? What is happening here?