couldn't guess format？is it a bug?

[busybeeCS]

recently,i find that vlc often fails to find correct modules when dong demux, it reports "couldn't guess format" after probe using avformat or it finds unsuitable module such as 'ps','mp3' which are not the real formats.
i tried to test with old version a year ago, the problem dont appear. i have no idea to solve this problem, is it a bug of new versions?
ps: i play with file access and media data comes from a pipe.

[edwardw]

Then it's a problem with avformat.

[busybeeCS]

Then it's a problem with avformat.

according to my tests, the problem exits for a year or more, looking forward to a proper solution