Quite possible
As I said, IANAL (I am not a lawyer), but if the license says you have to do so and you don't, it is most probably a copyright violation.
Of course it only starts to be a substantial problem if someone actually complains, but you never know.
For example an example I was just told about, Bukkit API and CraftBukkit which was some plugin or extension or something. Bukkit API was GPL, CraftBukkit used something from it / copied something from it and was released under LGPL. Then some Bukkit API guy was pissed and sued CraftBukkit which then did some strange surviving tactics I don't remember. Something so that the user has to provide the correct things instead or similar, something to not anymore violate the GPL of Bukkit API.