I've discovered what I think is a very serious bug. It just happened to me with v 2.131 but I think happened before with an earlier version.
I used autodetection in a directory full of movies. Since the movies are dubbed into spanish, most of the detected ones were incorrect (the name of the file is the title translated into spanish), and so in a manual process, for each one I change manually the movie and select the appropriate banner (with the spanish title). I did that for a number of movies and then, when selecting the banner for "El Reino Prohibido (2008).avi" (the forbidden kingdom), MC gave me a .net error; tried "continue" a few times but didn't work, so I selected "exit". But then, the avi file and the nfo file do not exist! there is the in the disk the "El Reino Prohibido (2008).tbn" file I was trying to save, but there is not "El Reino Prohibido (2008).avi" nor "El Reino Prohibido (2008).nfo", both seem to be erased. Since the path is in a network share, there is no undelete possible (the file itself is not a big problem, I will simply recreate it again from DVD).
A few days ago, I saw a .tbn file without the corresponding .avi/.nfo files, I thought at the moment it was me whom maybe had deleted them by mistake, but now I think it was another deletion by MC, since it was in the directory I process the movies with MC and there has been some .net errors from time to time.
There is no log nor anything, since I noticed the missing file after launching again MC several times, but I am sure MC is the culprit here, since there is the .tbn file but no .nfo nor .avi and I am the only one accessing the network and haven't executed any other program but MC. Sorry if I cannot be more specific, and of course I have no idea on how to reproduce the bug, but please take a look at it since I think it is very serious, it can delete an irreplaceable file by mistake! The only clue I can give is that the error appeared when manually selecting the poster file.