transcode h264 inaccurate frame rate

First, I post here in the hope that it will be useful, I am not an expert... It seems there is some kind of bug while transcoding to h264... I already posted in the VLC forum but without any answer...

http://forum.videolan.org/viewtopic.php?f=4&t=107536

http://forum.videolan.org/viewtopic.php?f=4&t=107619

I use this code to transcode from AVI to H264:

vlc.exe file.avi --sout=#transcode{venc=x264{profile=baseline},vcodec=h264,vb=800,acodec=mp4a,ab=128,}:standard{access=file,mux=mp4,dst=TEST_enc.mp4} -vvv

Doing so, the resulting file has a few missing frames at the end... Also the frame rate reported in VLC codec information is inaccurate...

Adding fps=25 does not help...

I also tried to append the same file twice (for testing purpose) using this code:

vlc.exe file_1.avi file_1.avi --sout-keep --sout=#gather:transcode{venc=x264{profile=baseline},vcodec=h264,fps=25,acodec=mp4a}:standard{access=file,mux=mp4,dst="file_out.mp4"} --sout-all -vvv

The resulting file has a length of 52s instead of 40s (and plays badly)...

It's a pitty, as VLC seems to have all the things I need to transcode to h264, + to append files, + add a logo (all this in one command line)... But I can not get a correct result...

Attached files that illustrate the above...

Thanks in advance for any help.