And from what I heard, grave sounded to much like 'duke' (in French or German), so the French Revolutionaries weren't too keen on it.
The French word for 'duke' would be 'duc' (pronounced more or less identically to the English word, for the obvious reason that the English word is borrowed from French). The German word appears to be Herzog. It's hard to see where either word might be plausibly confused with any possible pronunciation of "grave".