Q. After hearing our Baal Korei attempt to read Mordechai’s name in the Megillah with the pronunciation of the Chataf Komatz under the Dales, I realized that he was pronouncing it like a Komatz. Ostensibly, a Chataf Komatz should not be pronounced like a Komatz, otherwise there would be a Komatz. (Is this correct?)

A. Minchas Shai (on Chomesh Megilos p. 127, Neviim Uksuvim p. 154, and other locations.) mentions that some maintain that there is a chataf-komatz under the letter daled of Mordechai.
Piskey Sh’muos (630) quotes Horav Sh. Z. Auerbach zt”l who opines that some would read it with a chataf-komatz, and that was tradition in Shaarei Chessed. However, he mentions that Horav Ch. Kanievski and Horav N. Karelitz Shlit”a disagree.
Boruch Mebonim (p. 135) explains that the tradition of some of Bnei S’farad was that only certain Mordechai names were read with a chataf-kometz)
Horav Shlomo Miller’s Shlit’a opinion is that those who do follow this tradition have to be careful to pronounce I correctly, as the change in articulation is slight.

Rabbi A. Bartfeld as revised by Horav Shlomo Miller Shlit”a