[x264-devel] x264 [error]: 2nd pass has more frames than 1st pass // dependant on input file?

[dubplate]

I have read other posts regarding this error.  I just want to ask why 
this occurs only with certain files when using following commands:

1st pass:
/usr/src/x264/x264 Iceage/input/iceage4-tlr1_h800p.mp4 --input-res 
1422x800 --pass 1 --slow-firstpass --profile baseline --bframes 0 --crf 
22 --no-cabac --trellis 0 --keyint 48 --min-keyint 24 --video-filter 
resize:width=480,height=270,fittobox=both --fps 24 --no-mbtree --weightp 
0 --no-8x8dct --threads auto --output ./Iceage/firstpass_write --stats 
./Iceage/Iceage_fp_base


2nd pass:
/usr/src/x264/x264 Iceage/input/iceage4-tlr1_h800p.mp4 --input-res 
1422x800 --no-cabac --me umh --subme 7 --merange 16 --scenecut 40 
--qpmin 0 --qpmax 58 --trellis 0 --no-8x8dct --weightp 0 --no-weightb 
--bitrate 590 --vbv-maxrate 590 --vbv-bufsize 14000 --video-filter 
resize:width=480,height=270,fittobox=both deblock 1:1  --bframes 0 --fps 
24 --level 3.1 --keyint 48 --min-keyint 24 --pass 2 --no-mbtree 
--threads auto --output Iceage/Iceage_B_3.1_576x324_590.mp4 --stats 
Iceage/Iceage_fp_base


x264 [error]: 2nd pass has more frames than 1st pass (3842 vs 3841)
x264 [error]: x264_encoder_open failed


Which filters am I setting incorrectly between both passes? As far as I 
understood this is related to different settings between both passes.