Eduardo, 
sorry for the Siemens-only prescription and forcing you to use a workaround to use sequential! That was a big oversight on our part and will be fixed in the next release.

As a side note, in case anyone else is having trouble with this but is using an odd number of slices, for using non-Siemens alt-asc, the Siemens alt-asc is practically identical when there are an odd number of slices, but when there are an even number of slices, Siemens is very different (starts on the second slice instead of the first) from plain alt-asc. So if you have a non-Siemens scanner and your acquisition is interleaved and you have an odd number of slices, the default is fine, but if you have an even number of slices, you'll need to modify to use plain alt-asc. Also, will be fixed!