Odd automatic ghostpad creation behavior with playsink

[Carlos Rafael Giani]

I am writing a bin element that is supposed to be used as an audio sink. 
Internally, there is an identity element, whose sink pad is ghosted in 
the _init() function. The identity pad is the "front", the entrypoint 
for audio data. I did this to make sure that the bin's ghost sinkpad is 
always linked to an existing element. During the NULL->READY state 
change, I then choose which internal sink element to create and use, and 
link that one to the identity element's srcpad.

This means that prior to the NULL->READY state change, the identity 
element's srcpad is unlinked. This worked fine in pipelines like 
decodebin ! my-sink-bin .

But then I tried to use my sinkbin with gst-play, and it didn't work. 
gst-launch-1.0 playbin audiosink="my-sink-bin" didn't either. It turns 
out that for some reason, the internal playsink recursively walks into 
the sinkbin and decides to create a ghost srcpad that is linked to the 
identity srcpad. Then, during the NULL->READY state change, linking the 
internal sink to the identity pad doesn't work, because the srcpad is 
ghosted.

I did a workaround by creating an initial fakesink and link it to the 
identity element. During the NULL->READY state change, I get rid of that 
fakesink and link the internal sink instead. This fixes the problem, but 
I wonder why playsink is doing this. Is this by design, or is this a bug?

Oh, also, I was using GStreamer 1.10.4 here (the packaged version in 
Ubuntu 17.04). I'll try with git master later.