Can't say i've ever noticed this!Maybe i will now that it has been brought up.As long as all the information and the callsign is read back in a manner that makes it unambiguous then it's fine by me. To be honest I find DLH one of the easiest airlines to work with,always professional and polite and with a near perfect level of English in an easy to understand accent.
What bothers me more is the increasing number of readbacks I get without a callsign attached at all! This is extremely common when transferring someone to another frequency-and is becoming more common when issuing control instructions.