In the new version 2 Alpha 4 (maybe also in older versions), I experienced a mix-up of the syntax highlight and the auto-completion (CTRL+SPACE) feature for Bibtex files and commands.
If I create a new bibtex file within Texniccenter, then auto-completion works correctly (starting to type @phdthesis and the entry type and all necessary items are created). But syntax highlighting is not working. A simple re-start of Texniccenter fixes this, then the syntax highlighting is working correctly for the new file.
If I open and use a bibtex file created outside (or saved previously in) Texniccenter, then the syntax highlighting works instantly, but the auto-completion is not working at all. Here, it doesn't matter if I restart Texniccenter or not, Bibtex auto-completion only works in newly created .bib files.
It generally works in .tex files, although there is no need to do Bibtex auto-completion in .tex files, I think.