I haven't done any device sync'ing in a long time so I don't know if this is a recent issue or not.
I'm using a client/server setup, client using the servers library. I setup MC to sync a playlist to a folder on my harddrive. In options I have set:
Simultaneous Conversions: 4
Mode: Convert unsupported formats
Encoder: MP3 Encoder
Apply DSP is not checked
Audio Path: [Album Artist]\[Album]\
Supported Types: mp3;aac
Playlist selected to sync with
Everything else is set at it's default. I add some flac tracks to the playlist. When I goto the device list it shows the tracks in queue. Now when I sync, the first 3 tracks in queue will say Downloading (even though I selected "Simultaneous Conversions: 4") and it will take much longer than it should for it to sync those 3 tracks. As one track completes it moves on to the next track, never processing more than 3 at a time. When it finally finishes I goto the folder the tracks were sync'd to and they are there and have been converted to mp3 format. However the files have no tag data with them. If I look at them in foobar2k it shows no tag data. If I look at the tracks in MC they also show no tag data. As well, if I rescan the replaygain values they are all like, .3 or .1 or -.25, like they have all had the volume leveling applied to them through the dsp, even though I have Apply DSP unchecked in the sync options.
All this only appears to happen if there is a conversion happening during the sync. Sync'ing mp3's seems to work fine as I have that set as a supported format. As a test I setup a local library and added some flac files to it and performed the type of sync again and that time it worked fine. So it appears to only happen on the client when setup as client/server. In Media Network options I have Audio Conversion set to "Don't convert audio" so the client receives the unaltered flac file.