It appears that the earliest explicit discussion of the correct pronunciation of the opening words of Kaddish is to be found in the Siddur of R' Shabbetai Sofer (Rashas, 16th cent - 17th cent. Hakdama Peratit Ch. 17, Vol. 1, ed. Satz, 5747 [1987]). Rashas argues that although in the Tenach we never find yitgadal (the Dalet having a Patach) nevertheless it is acceptable to read it this way as we find yitgadaal (the Dalet having a Kamatz) which is the pausal form of yitgadal (the Dalet having a Patach). He then proceeds to say that as we also find yitgadel, that form is preferable. Prior to the Satz edition Siddur Rashas was rare and not well known.

R' Zalman Hanau (Razah, 1687-1746) refers to works attributed to students of Rashi to support the proposition that it should be yitgadel veyitkadesh (Binyan Shelomo quoted by Chaim Cohen in 'Yitgadal veYitkadash,' Masorot Vol. 8, Hebrew University, Jerusalem, 1994; also reproduced in: Luach Eresh p. 340). Furthermore in Shaarei Tefilla (73) he argues that Tsere is the appropriate vowel-sign for the second letter of the root for Hitpa'el in general, making it a grammatical issue rather than the style of a particular word. He writes 'Titbarech Tzurenu - the Resh has a Tzere as this is the preferred form for the Hitpa'el conjugation … and even though we have found a few with Patach such as … these and those like them follow Aramaic grammar, for the books of Scripture sometimes follow Aramaic grammar, as in … It is not right to mix this language in our prayers "for a man should not request his needs in Aramaic" (TB Shabbat 12b, Sotah 33a).' (Shaare Tefilla 73, in Luach Eresh p. 249) (This is an extreme form of Hebrew purism. Razah is arguing for a purity of Hebrew that, he admits, is not to be found even in the Bible! Does the intrusion of Aramaic phonetic forms turn Hebrew words into Aramaic? In the following generation, Hebrew purism became a fetish of the Maskilim.)

R' Yaakov Emden ben Tzevi (Yaavetz) responded to Razah's attacks on the traditional form of the prayers which he regarded as a general attack on Jewish tradition (see the end of his introduction to 'Luach Eresh B on Avot' where he suggests that the novel forms of the prayers are related to the novel practices of men shaving their beards and women uncovering their hair). He argues that the works attributed to students of Rashi do not support the proposition that yitgadel veyitkadesh should be read with Tzere, as 1) their authorship is doubtful, furthermore 2) they deal with the meaning of the words rather than with their pronunciation. He goes on to argue that even if we were to admit that his arguments had substance - which they do not have - this would be insufficient to change 3) that which is established in the mouths of all (Luach Eresh 257, pp. 96-97). 4) This is the Hebrew of the Sages not that of the Bible.

Hasagot of R' Mordechai Dusseldorf (Luach Eresh p. 341-2) also attacks Razah on similar grounds. R' E. Landau (author of Noda Bihuda) in his Haskama to these Hasagot, wrote that Razah 'changed a number of things bezadon ('with malice') … and one should not rely on his innovation'. R' Seligman Baer (editor of the siddur Avodat Israel) also attacked Razah (Luach Eresh p. 497) making a number of arguments in favor of yitgadal veyitkadash and referring to his teacher R' Wolf Heidenheim who also argued for this form.

Mishna Berura (56:2) states that the reading with Tzere - yitgadel veyitkadesh - is correct and refers to the Peri Megadim as the only source. The Peri Megadim (Mishbetzot Zahav, 56:1) states this in the name of Razah! Did the author of the Mishna Berura have the other sources on this subject?

Chaim Cohen ('Yitgadal veYitkadash,') claims that the reason the reading with Tzere - yitgadel veyitkadesh is spreading among followers of the tradition of the 'Litvish Yeshivos', is because the Mishna Berura accepts it.

This may be so, but do the Litvish Yeshivos always follow the Mishna Berura? Do they say lizman hazeh (Lamed with Chirik) (MB 676:1; also Magen Avraham referring to Maharshal & Mate Moshe). What else is at work here?