When using command blocks to place dispensers using a command like so:
/setblock ~2 ~ ~ dispenser 2
where a block is blocking the front of the dispenser, the dispenser will be instead spawned facing the opposite direction.

I ran into this bug wanting to refill dispensers with exp potions to face bookshelves in an 'enchantment table room'. The bug seems intentional, although I feel like it only makes sense to let the user do what they want in this case