When I press a reset/power off switch on the MPC5748G-LCEVB, The program is erased and should flash manually again. I've flashed a basic "toggling a LED" code.
Is there any hardware or software configuration that I'm missing out ?
To me it looks like you does not load the code in the flash, rather then into RAM.
At leas the description looks like it.
Flash is not erased on reset, if the SW is not desired to do so.
Other possible explanation is that you see the SW only in the debugger, and it is not loaded in the chip.