This seems indeed to be the case for all Siemens scanners. If the protocol specifies 'interleaved' under "Series" it is by definition taking interleaved slices in the ascending order (1,3,5..., 2,4,6,...). As already indicated it starts with 1 if the number of slices is odd and 2 (2,4,6..., 1,3,5...) if the number of slices is even.

Maarten