digitalWrite() unnecessarily activates the pull-up resistor on the specified pin.

the issue with the pull-up in digitalWrite(),
(other than the fact that this line shouldn't be there),
is because the pin configuration register (PINCFG) isn't logically ORed with the bit mask when the pull-up bit (PULLEN) is enabled,
instead the mask is copied directly into the register.
This effectively clears all the other bits in the register including the input enable (INEN).

in addition this issue makes the code not forward/backward compatible to AVR code
(digitalRead therefore cannot read back the current value of a digital PIN configured as OUTPUT.)

--> https://forum.arduino.cc/index.php?topic=367517.msg2534096#msg2534096
--> http://forum.arduino.cc/index.php?topic=334073.msg2306580#msg2306580