I do not see this as an issue at all, leave alone its being a crucial one. When they convert thinking that they wll be able to shed their castes and the baggage related to it, why should they get benefits of the baggage after conversion?
Also, as far as I know, Christianity does not have or permit castes. Ask the pope in case of queries and concerns. Therefore, the term "Dalit Christian" is a misnomer.
