Hey Juanca,
Back in Lion, the way DS provides a recovery partition that it's captured led me to not be concerned with having the recovery partition generated by InstaDMG. Recently, finding that it's a simple thing to enable, the fact you'd probably want to have an updated recovery partition available for FileVault, and after a handful of root ownership questions with just HFS+ (that I haven't noticed in my testing) convinced me to turn on its creation as the default behavior. You can hard-code revert the change to turn it back by modifying line ~745 in instadmg.bash to once again use the HFS+ sparseimage format when generating a fresh BaseOS cache.
I've felt it is worth allowing this in the meantime and will revisit a cleaner way to disable it through choiceChanges/installerChoices, but I probably not in the near future between MacTech and other traveling.
Allister