R. Akiva Eger (on Shulchan Aruch 559:3) cogently argues that one should never recite kaddish between maftir and haftarah, as such an interruption would mean that one does not fulfill the requirement for the one who reads the haftarah to first read from the torah.
This is based on Shulchan Aruch and Rema 282:5 (as explained by Magen Avraham) who rule that one cannot recite kaddish after the seventh aliyah on shabbat morning and proceed immediately to read the haftarah (even bedi'avad), for this very reason.
R. Akiva Eger is therefore puzzled by the common custom to recite kaddish between the third aliyah and the haftarah on the morning of Tish'ah beAv. Nevertheless, commmon ashkenazi custom is indeed to recite kaddish at this point. (See e.g. here.)
What defenses of the common custom (against R. Akiva Eger's arguments) have been offered? How do we reconcile the custom to recite kaddish immediately before the haftarah on the morning of Tish'ah beAv, with the ruling of Shulchan Aruch and Rema the one cannot recite kaddish after the seventh aliyah on shabbat morning and proceed immediately to read the haftarah (even bedi'avad)?