So basically here's how the camera works:
* The camera tries to be at a specific vertical and horizontal distance behind the player. If it is not at that point, it will try to move to that point -- if I'm not mistaken, it's done by warping to a position between the camera's current position and its destination position (with cam_speed determining the interpolation amount). This means, so long as cam_speed isn't 1.0 or higher, the camera will always lag behind the player by some amount before reaching its resting position.
* The camera is a tangible object, meaning it cannot move through terrain (unless the terrain is specifically flagged as camera intangible).
* If the camera can't see the player (it is blocked by terrain), it will teleport directly to the player object's coordinates.
* In Standard (Analog and Simple appear to be different) the player's movement inputs are input relative to the player's angle, which is NOT the same as their current camera position. If the camera is not directly in line with the direction the player is facing, the player's movement input will not be oriented in terms of the camera position, i.e. movement input will feel like it's being rotated by some amount.
This is nothing that we've ever touched, it's just how Doom's thirdperson cam has always worked. It's only more noticeable now because we had recently increased the default cam_dist setting to rest the camera farther behind the player. Generally speaking, the farther away the camera is from its target, the more likely it is for certain awkward behavior to take place.