Megadrive 60hz mod

I was just trying to mod my Megadrive to 60hz mode (no switch, just a permanent mod), so I found some instructions and cut the JP3 bridge, to get my MD out of 50hz mode. I had not yet soldered the Jp3 to Jp4 line, which is supposed to get your megadrive into 60hz mode, but I decided to hook it up and give it a try.

Surprisingly, it ran in something very much like 60hz mode! I tried it with a PAL Sonic cartridge, and it ran in B&W (i'm using RF), had no borders and ran faster!

When I took a small piece of wire and bridged JP3 again, it instantly reverted back to running slower, with borders and in color!

Beats me why this all works! According to my instructions, you need to cut JP3 and connect JP3 to JP4. :huh
I am no technical expert (ahem) but perhaps as soon as you "cut the JP3 bridge, to get my MD out of 50hz mode", it reverts to 60hz mode since it is not running at 50hz anymore? Again I am no expert on modding, although I would really like to improve my soldering skills.