Filter chain and multiple outputs causing funky amounts of buffering after updating FFmpeg:

Relevant visible messages:
[out_#0:0 @ 0x7f38bc02f340] 100 buffers queued in out_#0:0, something may be wrong.    
[out_#1:0 @ 0x7f38bc02f600] 100 buffers queued in out_#1:0, something may be wrong.
[out_#2:0 @ 0x7f38bc02f980] 100 buffers queued in out_#2:0, something may be wrong.

has been broken for a while:
/usr/bin/time -v \
  ffmpeg -v verbose \
  -filter_complex "testsrc2=r=24:d=10:s=1280x720,split=4[video_input0][video_input1][video_input2][thumbnail_input];[video_input0]scale=3840:2160[output0];[video_input1]scale=1920:1080[output1];[video_input2]scale=1280:720[output2];[thumbnail_input]select='eq(key\\,1)',fps=1/60:round=up:start_time=0[thumbnail_output]" \
  -map '[output0]' -f null pipe: \
  -map '[output1]' -f null pipe: \
  -map '[output2]' -f null pipe: \
  -map '[thumbnail_output]' -f null pipe:
# Maximum resident set size (kbytes): 3989868

used to work (at a9a92682dd72b2593b79b099f96042c73f8694d2 for example), but nowadays works like the filter_complex only case:
/usr/bin/time -v \
  ffmpeg -v verbose \
  -f lavfi -i "testsrc2=r=24:d=10:s=1280x720" \
  -filter_complex "[0:v]split=4[video_input0][video_input1][video_input2][thumbnail_input];[video_input0]scale=3840:2160[output0];[video_input1]scale=1920:1080[output1];[video_input2]scale=1280:720[output2];[thumbnail_input]select='eq(key\\,1)',fps=1/60:round=up:start_time=0[thumbnail_output]" \
  -map '[output0]' -f null pipe: \
  -map '[output1]' -f null pipe: \
  -map '[output2]' -f null pipe: \
  -map '[thumbnail_output]' -f null pipe:
# from Maximum resident set size (kbytes): 66176
# to Maximum resident set size (kbytes): 3990648