Problem with Arduuino to breadboard Mega8
I found here: https://www.arduino.cc/en/Hacking/Bootloader?from=Tutorial.Bootloader 

that NG / mega8 bootloader doesn't enable the rx pin internal pullup nor it gets out of the bootloader even if receiving junk data on rx  (which was my case due to leaving it open thus floating). It also has a delay of 6 to 8 seconds intentionally. 

Probably I'll use another bootloader since the link to source code on the page was broken or just program the L version without any bootloader and better fuse options.