What is the difference between MCLR and switching VDD OFF-ON?

[Demon]

16F18877
MeLabs U2 USB programmer
Breadboard powered from wall adapter.


I just spent an ungodly amount of hours tracking a problem, turned out MCLR was NOT making a "complete RESET". I had to power down the breadboard and turned it back on for programming to take effect completely.

DAT and CLK only used by MeLabs programmer

Standard MCLR circuit:
- MCLR pin on PIC to 10K to VDD
- MCLR pin on PIC to 100R to MCLR on MeLabs U2 USB programmer
- MCLR pin on programmer to pushbutton to VSS

Power:
- 12V Wall adapter to rocker switch (VDD)
- rocker switch to DC-DC converter
- DC-DC converter to breadboard

My CONFIG in case it's relevant:

#CONFIG
    __config _CONFIG1, _FEXTOSC_OFF & _RSTOSC_HFINT32 & _CLKOUTEN_OFF & _CSWEN_OFF & _FCMEN_ON
    __config _CONFIG2, _MCLRE_ON & _PWRTE_OFF & _LPBOREN_OFF & _BOREN_ON & _BORV_LO & _ZCD_OFF & _PPS1WAY_OFF & _STVREN_ON & _DEBUG_OFF
    __config _CONFIG3, _WDTCPS_WDTCPS_11 & _WDTE_OFF & _WDTCWS_WDTCWS_7 & _WDTCCS_LFINTOSC
    __config _CONFIG4, _WRT_OFF & _SCANE_available & _LVP_OFF
    __config _CONFIG5, _CP_OFF & _CPD_OFF
#ENDCONFIG