In a few areas, however, Berber loans retain the Berber nominal prefixes a- and ta-, and hence stick out like a sore thumb. In such cases, they often keep Berber-style plurals as well, reproducing a Berber subsystem within the otherwise Arabic domain of the dialect's nominal morphology. The only major Saharan dialect that consistently does this, as far as I know, is Hassaniya in Mauritania and the Western Sahara. However, during fieldwork some years ago, I came across another case well outside of Hassaniya. The area around Adrar (medieval Touat), in southwestern Algeria, seems to have shifted from Berber to Arabic relatively recently, and the process is not complete even today. At least one village, Beni-Tamer just outside Adrar, accordingly borrows many Berber nouns with Berber nominal prefixes, including ones unfamiliar to other speakers from near Adrar that I met. I only spent a short time with the one speaker from Beni-Tamer that I met, but he gave me quite a few examples from his Arabic (he did not speak Berber):
With masculine a-:
- aždəl "garden near town"
- ažəlžim “hoe” (Taznatit ažəlžim)
- afdam “palm fibre” (cf. Hassaniyya fdām)
- afrag “palm-leaf fence” (Taznatit afrag, cf. Hassaniyya efəṛṛāg)
- aqənnin / qənnin "palm stump" (Taznatit taqənniħt)
- agžəm “cellar” (Taznatit ikzəm)
- amazzər “sloped spot in an irrigation channel”
- anfif “drainage hole” (Taznatit anfif)
- tadmayt "garden outside town"
- tasgat “large basket” (Taznatit tasgawt)
- taṣəṛbiṭ “skink”
- tagəmmi “stable”
Have you seen anything similar in a dialect you're familiar with?
References: Hassaniyya from Taine-Cheikh, Dictionnaire hassaniyya-français; Taznatit from Boudot-Lamotte 1964, "Notes ethnographiques et linguistiques sur le parler berbère de Timimoun".