This is for JabRef 2.9.2 on linux but also relevant on the windows release.

I often work with reference libraries that must be used on both bibtex only journals in addition to biber/BibLaTeX. Until recently, I didn't have a problem with this under JabRef. (My students also noticed this problem.). The problem is how the Month field is formatted. If you put the month field to "March" or "mar", Jabref will always put {} around it.

This is a problem because biber/BibLaTeX can only deal with the short version without brackets. If you put "{mar}" it continues to skip the entries because it cannot convert them into the numeric representation. It has to be "Month = mar," or biber just returns an empty bibliography.
This has been mentioned in http://tex.stackexchange.com/questions/27898/biblatex-month-field

When BibLaTeX mode is enabled, you can't make a month field, only a date field, which is a problem for these older templates, which I don't have control over.
Please help. I don't want to have to edit the file manually to create the Month field.