From what I've read and listened about the janissaries, they were individuals captured as slaves from Christian Europe (often from Orthodox Greece or the rest of the Balkans). Somewhere along the process, the vast majority of them become perfectly good Ottoman Muslims, loyal to the Sultan--never mind their past lives and heritage. When they inevitably fought for the Ottoman Empire against Christian rival powers along the western frontier, what were their thoughts about their ethnic and religious (ex-)cousins, and how did those "cousins" see them? Were there any recorded instances of janissaries reverting to their old heritage--or at the very least experiencing mental conflict--after confronting such cognitive dissonance?
Were there any recorded instances of janissaries reverting to their old heritage--or at the very least experiencing mental conflict--after confronting such cognitive dissonance?
Maybe this doesn't really answer your question, but the devshirme recruits, including janissaries often remembered and retain their heritage. By the 17th century, most of the devshirme recruits were teenagers, usually 14 to 18 so there are indications that devshirme recruits retained various elements of their early background other than merely in the sphere of religion. They remembered their birthplace, families, native languages, and customs and exhibited a special tie to it. Ottoman writers called this phenomenon cins, ethnic-regional solidarity among Ottomans with the same background. For example Koprulu Mehmed Pasha built a mosque and school in his village of Ruznik in Albania, which he refers to as his original home. Grand Vizier Sokollu Mehmed Pasha (who also served as a janissary soldier for some time) built the famous Dirna bridge in his hometown of Bosnia. He also helped his family members on attaining higher posts, by patronizing his cousin (or brother) Makarije Sokolovic as the patriarch of the restored Pec Patriarchate, a post that the Sokolovic family will hold for years. This system of patronage becomes rather ubiquitous in the 17th century, another example is the Georgian Sipahi Gurcu Nebi is a brother of Cafer Pasha, a cavalry commander who later become the agha of the Janissaries. It is also told that Sinan Pasha dismissed the Janissary agha Mehmed Pasha because he was Bosnian, and replaced him with an Albanian Yemisci Hasan Pasha.
Language and customs are also element of the original background of an recruit that he might retain. While all recruits learned Turkish language and customs there are indications that the original language and customs was not forgotten. For example, Mere Huseyin Pasha a grand vizier in the 17th century would sometimes speak Albanian, and the order he give for a removal of a guilty person "mere" meaning "take him" stuck as his nickname. Ismail Pasha, in the same century would also start talking with a strong Bosnian accent when under stress. His political rival Seydi Ahmed Pasha were also known to swear in Circassian when he's angry. Ibsir Mustafa Pasha was also known to dress in Circassian style. These suggest that many retained their original language and customs, or at least certain elements of it. It does not seem unreasonable to think that two Ottomans of, say, Circassian origin would converse in their native tongue if they happened to be by themselves.
Bibliography:
Ethnic-Regional (Cins) Solidarity in the Seventeenth-Century Ottoman Establishment by Metin Kunt
Bureaucrat and Intellectual in the Ottoman Empire: The Historian Mustafa Ali by Cornell Fleischer
The Encyclopedia of Ottoman Empire by Gabor Agoston et al