Selecting an audio stream with select-tracks-for-object signal has no effect

I am using GStreamer 1.18.1 on Windows mingw x64. The issue is that I'm attempting to use the select-tracks-for-object signal on GESTimeline to choose 1 from among 4 mono audio streams in my test file, but no matter which audio stream is chosen at runtime, only the first one is ever included in the output. I've put together some sample code that reproduces the issue. On line 34, changing the target_stream should select between the various audio streams (but doesn't currently). Make sure to set line 122 to the location of the video file.

main.cpp 1080i-_4_Ch_1-Dialogue_2-Nat_3-Music_4-Tone_30sec.mxf