Dispenser shooting arrow in stairs

For some weird reason, when you place stairs in front (like the image bellow), the arrows that are thrown of the dispenser are given to a player in a certain distance from the dispenser (I will try to upload the image showing where it can be collected).

It also happens with steps.

The red rectangle is the area where you can collect the arrows, and the dispenser is in the middle of those iron blocks (bellow them there is a high speed redstone repeater)