Clementine 1.2.3 Windows version currently cannot play Opus files (.opus), giving an error "Your GStreamer installation is missing a plug-in".
If I extract libgstopus.dll and libopus-0.dll from GStreamer SDK and put them into corresponding Clementine directories, Clementine will play the files.
Tried that release (1.3.0 RC 2). It has the same error.
I also tried 1.3.2 RC 1 (from the page you linked), and that version failed as well -- except not just on Opus files, it also failed on regular mp3 files.
Clementine 1.2.3 Windows version currently cannot play Opus files (.opus), giving an error "Your GStreamer installation is missing a plug-in". If I extract libgstopus.dll and libopus-0.dll from GStreamer SDK and put them into corresponding Clementine directories, Clementine will play the files.