I use Media Jukebox for a month and I must say that I like it because it fulfills my needs and it is sleek, clean and quite light for its category.
Nevertheless, a few days ago, I reinstalled from scratch the application (I even manually removed the J River Application Data folder and the user-dependent Regedit settings) and now I've noticed an odd bug(?) related to the last.fm plugin. Everything worked as expected before the reinstallation. I don't know the build number of the application but it is the version 12, downloaded a few days ago. No other softwares have been installed between the unintallation and the reinstallation process.
No track is submitted to last.fm unless the last.fm main 'screen' is focused (Services & Plug-ins->last.fm; the window that displays the list of the tracks submitted). By focused I mean currently displayed but the application can be minimised, visible or in full screen: it doesn't matter. If any other Media Jukebox 'screen' is in use (e.g. Playing Now, Audio, Start, etc) instead of the last.fm one, the song playing in the background IS NOT submitted to last.fm. The logs show that actually no track is queued up whereas all of them are played for more than 3 minutes.
This is not a problem specific to a track played (i.e. incompatible format, no tag, etc) because the sames tracks have been used as a test and are either submitted or not according to the situation described above.
An interesting note: all songs successfully queued are cleaned up from the last.fm window if one switches from the last.fm screen to another and back. If I remember correctly, this is not supposed to happen.
Thanks for your help troubleshooting this.