Without checking my references, I believe it was not uncommon for a 'Friedrich' to have the right (starboard) side small triangle be of metal. In fact, it appears to be the norm. Just check the following site and you can find plenty of such cases:
http://www.bf-109.de/
Here is only one such occurrence:

[Source:
http://www.bf-109.de/
Foto-ID: 2073]