It seems that when setting the number of times a mailing should be sent, i.e. when you set repeat schedule <variable> times. it is parsed as the number put in. I am guessing, although I'm not familiar with perl, that it is 0 based, so when you say 3 times, if the number 3 is used as the variable in the for loop (or whatever perl uses), it will actually send 4 times.
running dada mail 3.0.4 stable
plugin version: ?