Square minifig torsos?

I just noticed something strange about the minifigs in the sets I've
bought lately: the roundness of the shoulders (upper corners of torso
part) varies greatly. While some are quite round (like they've always
been), others are less so and some are almost square, with only a very
slight rounding of the edges.

I checked the sets I've bought the last months:

7245 (prisoner transport): Prisoner has classic torso, while officer
has the almost square one.
4753 (Sirius Black's Escape): Sirius has a medium rounded torso, while
Harry Potter has the classic one.
4766 (Graveyard duel): Harry Potter has classic torso, while the
two-faced guy has a medium one. The rest (including the dark angel on
the tombstone) has square torsos.
7015 (Fenris wolf): Viking has a square torso.
7242 (Street sweeper): Operator has classic torso.

Has anyone else here noticed this? I think it's quite strange,
especially as it varies within a single set. Is there a reason for
this, or is someone asleep at the quality control?

Axel
Norway