I think I see the source of the confusion.

We have to consider the mechanics of the game if there were to be late surrender in an ENHC game. The player would surrender, but the action would not be resolved right away. Instead some sort of marker would probably be placed on the initial bet. Therefore, at the time of the surrender action, the EV is the sum of

3/49 x -1 = -0.06122 --- the dealer eventually draws an ace for a natural and the entire bet is lost despite the attempt to surrender
46/49 x -0.5 = -0.46938 --- the dealer does not draw an ace and we lose only half of our bet

The EV for surrendering is -0.5306 as k_c proposes.