Comment 3 for bug 690296

Using x264 2:0.98.1653+git88b90d9-3 directly doesn't reproduce this behavior on x86_64:
x264 --bitrate 1000 -o test1.h264 IronMan.mkv
x264 --crf 20 -o test2.h264 IronMan.mkv

Compiled x264 0.110.1820 fdcf2ae:
x264 --bitrate 1000 -o test3.h264 IronMan.mkv
x264 --crf 20 -o test4.h264 IronMan.mkv

13M test1.h264
72M test2.h264
13M test3.h264
72M test4.h264

However, there is a difference between the repo and compiled FFmpeg:
Using FFmpeg 4:0.6-2ubuntu6 and libx264-98 2:0.98.1653+git88b90d9-3ubuntu1:
ffmpeg -i IronMan.mkv -an -vcodec libx264 -vpre medium -b 1000k -threads 0 1b.mp4
ffmpeg -i IronMan.mkv -an -vcodec libx264 -vpre medium -crf 20 -threads 0 1crf.mp4

FFmpeg SVN-r25943 and x264 x264 0.110.1820 fdcf2ae:
ffmpeg -i IronMan.mkv -an -vcodec libx264 -vpre medium -b 1000k -threads 0 2b.mp4
ffmpeg -i IronMan.mkv -an -vcodec libx264 -vpre medium -crf 20 -threads 0 2crf.mp4

290M 1b.mp4
72M 1crf.mp4
13M 2b.mp4
72M 2crf.mp4

Sample: http://mirror05.x264.nl/Dark/x264clips/