So Char A has no chance moving a few feet to D, because he hasn`nt perform a "disengage from melee" maneuver and because the taken hits?
Disengaging from Melee means "removing oneself from melee completely". Taking a step or two in order to change and/or confront another foe is NOT "Disengaging from Melee", it is simple movement (and maybe attack).
Now the specifics of this movement may put the character in greater danger from the foe he was facing, but that depends entirely on the situation at hand, and the actual movement performed.
Remember, all combat involves movement, some back and forth. An intelligent combatant can easily direct this movement in the direct he wants to go by giving ground as his foe advances (trying to force foe in a specific direction where you are not leading (by giving ground) is a bit trickier and likely to require a roll of some sort).