How to recreate
Using a Mac, start Factorio
Load any map or make new one
Press Command + W, A, S, or D

Result
Player will move in the direction previously pressed forever without any additional input.

Fixes
Press previously pressed direction key without Command key.
Restart Factorio, not ...

It seems like the game is very playable with a mac now. I just ran into the problem of renaming a train station and so pressing Command + A to select all the text which also made me move to the left constantly and I couldn't figure out why but found the fix here: pressing A again. Should I post this ...