Intrachromosomal duplications can be generated from overlapping inversions as shown here.
When meiotic recombination occurs within the region shared by overlapping inversions, the resulting chromosomes will be duplicated or deleted for the regions between the two left breakpoints and the two right breakpoints. A chromosome can have two duplications, two deletions or a deletion and a duplication depending on the relative positions of the breakpoints.
Because deletion and duplication of centric heterochromatin is usually inconsequential, inversions with proximal breakpoints located in centric heterochromatin are often used to simplify this approach.
The symbols for the resulting chromosomes reflect the left side of one inversion and the right side of the other as shown above. Sometimes Df or Dp synonyms are substituted for these complicated symbols. For example, Dp(2;2)Cam2 was originally called In(2LR)DTD24[L]DTD8[R].
And for you chromosome geeks...
Many intrachromosomal duplications of this type were made from pairs of pericentric inversions using autosynaptic intermediates. The method is conceptually equivalent to the figure above, so you don't really need to know the details, but, if you're curious, it is really, really cool genetics! See chapter 20 of Drosophila: a laboratory handbook and Gubb (1998).