Backwards compatibility to Bibtex gone?

I use Biblatex in my own documents, but sometimes I am a co-author with someone who still uses Bibtex. I now have the following problem: My Jabref-File has the field “Journaltitle” which is not recognized as Journal if I use Bibtex in a LaTeX document. Am I doing something wrong or is this really not backwards compatible?

Hi Renger,

JabRef supports both BibTeX and BibLaTeX, where BibLaTeX is the successor of the original BibTeX.
The Field Journaltitle is a BibLaTeX field, while journal is from BibTeX. All fields are treated independent.

In Biblatex mode, the field Journal is in the Other fields tab.

As long as you don’t use the CleanUp operation ("Convert/Move entrys to Biblatex fields) you can have values in both fields parallel.
Addtionally, you can change the mode of the database, by toggling between BibTex/Biblatex (File-> Switch to BibTex/BibLaTex).