I've had a look and checked the D925 service manual to confirm what you are saying and from what I can tell it looks like Moth3r is correct (as usual). According to the block diagram in the manual, the video for the Scart connector comes from exactly the same point in the circuit as the standard composite plug. The composite video is then fed back from SCH4 to SCH3 and eventually back to the Audio board (SCH2). This is probably to keep the wiring to the scart connector all neat and tidy inside the player. It's most likely that you're looking at the audio board, which has all of the scart connections on it for Audio/video etc. There is no additional processing done to the composite signal from when it leaves the point at the Composite plug, all the way across the 3 circuit boards listed and out through the SCART connector. The composite output is exactly the same as that on the SCART connector.

Hope this helps.