Hi Yoann,
Yes, Distribute evenly spaces the centerlines of symbols/groups so may not give you the result you desire when those objects are of different sizes in the distribution axis.
However, we don't really recommend using Distribute in Block Schematic drawings because it's much more important that Symbols - and therefore their input and output stubs - are
exactly on gridpoints so that Cables will align neatly.
If you Distribute 3 objects then there's only a 1 in 3 chance that the IO stubs will be on the grid after Distributing, and this only gets worse the more objects are Distributed (it's 1/n that the results will be on the grid).
I hope this makes sense.