check to see if the "optimize container for interactive content" setting is checked under the inspector.
Not sure I completely understand what the issue is though. If you're able to place another container that is fine, why not just change that to the field you need?
I had similar problems after installing FM Server 13.
I was able to get the required behaviour by setting the container field to optimise for images. The container field then showed a small .pdf icon which I canopen with a button that exports the content to the temporary folder as required.
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