.flac file extension showing in Title

Apologies if this is answered elsewhere but a google and mp3tag forum search have not revealed the answer to me.

I have two main folders on my network under 'Music'

Music > FLAC

Music > MP3

Taking one example file in the FLAC folder:

Filename - 01. Hold On.flac
Tag - FLAC
Title - Hold On
etc.

and the same track in the MP3 folder:

Filename - 01. Hold On.mp3
Tag - IDV32
Title - Hold On

If I look at the MP3 track via a UPnP device, it will display as:

Hold On

Boys & Girls


etc. (depending on the device)

If I look at the FLAC track on the same device, it displays as:

Hold On.flac

Boys & Girls


etc.

All my FLAC tracks display as TITLE.flac - why is this and can I remove the .flac part?

I've checked that it is definitely TITLE being displayed by renaming the filename to something completely different and it still displays as TITLE.flac on the network.

I'm hoping there is a simple answer to this but my searching has found nothing remotely connected so far.

For added info, I am running a Synology DiskStation NAS running DSM 5.2 if this may be a factor.

This issue does not have anything to do with the filenames or tags. So it is not solved by renaming or changing tags. Your issue is caused by your player. Many DLNA/UpNp players do odd things with FLAC or any non mp3. To solve the problem you'll have to find a way to change settings in your player or change players altogether.