Long discussion about this on the Goat.
The baseline reason for the change was that the supplier decided that they would switch the shape of the tin, its as simple as that. This obviously keeps their costs down as producing/purchasing two different shaped tins is more expensive than one.
The technician training comment is valid up to a point. People make mistakes that they didn't intend to commit; you cannot train/order/threaten human nature out of humans, its been tried and it doesn't work. Anything that can make the liklihood of mistakes happening must be for the better; having two regularly used fluids in different shaped tins is one way of so doing.