Users of language, whether native or foreign, differ in the degree to which they are aware of what they say phonetically and grammatically. Thus non-native speakers are often unaware of making mistakes and do nothing to correct themselves even when exposed to repeated exemplars of the correct forms. But this is also true of native speakers, particularly when confronted with variation and the necessity to choose the correct variant.
An example of the latter phenomenon was heard this week from President Obama in connection with the G8 economic summit being held in L’Aquila, Italy. The latter town’s name in Italian is pronounced with the stress on the initial syllable. Mr. Obama must have heard this pronunciation numerous times, but he (and some others on the radio) mispronounced it, putting the stress on the medial syllable. It is perhaps not surprising to hear this from a speaker of English who speaks no foreign language and generally seems to be uncomfortable with foreign onomastic items. But in the face of ample evidence to the contrary, a speech habit that goes against such evidence can only be chalked up to a lack of verbal proprioception, a strange defect in someone who is (otiosely) praised for his rhetorical skills and does not lack for education.