Long ago in Texas, the federal courts applied the Texas Rules in deciding disqualification motions; then, two disqualification motions were filed in Texas federal courts which resulted in two opinions from the Fifth Circuit holding that "federal law" -- not state disciplinary rules -- control disqualification motions in federal court. That holds true even if, as was the case, the local rules of the district court specifically adopt the Texas Rules as the rules governing ethics. I've always wondered why it is that whether something is ethical, or not, depends on whether a federal court has subject matter jurisdiction, but that has not stopped this body of law from growing, with the latest case to be In re Kennedy, 2008 WL 1052039 (Bankr. D. Neb. Apr. 8, 2008) (case wasn't posted to the court's website, yet)
This funky choice of law issue creates some amazingly complex problems in Texas practice, since sometimes there is no discernable "federal law" on an ethics issue, and, compounding things, the Texas Rules often differ from the Model Rules and Restatement, which are sometimes viewed by Texas federal court as stating the "national standard" that is "federal law." What do you do if the case is about to be filed, but in state court, but is removable, for example?
To tie it to another thread here, I know that sometimes California's federal courts follow California rules, while sometimes they don't!