Doomsday Engine

In that case it could be related to how/when the Strafe modifier state is updated. We'll need to investigate...

I would guess this is related to the sharp event processing. Logically the modifier states should only change on sharp tics if input-sharp = 1

To offer some more information regarding this;

It turns out that pressing the Alt Key while playing, no matter if anything is bound to it, causes Dday to jitter for me.

It seems this may be an artifact of QT on Windows and that Dday disables the default behavior of the Alt Key opening the application menu.

This may have led me to erroneously believe there was an issue with the Strafe/turning toggle key in Dday. By default (In Dday and Vanilla) and in my control scheme, this is bound to Alt.

I'll also tie this report to the other issue the Alt Key seems to cause with Dday on Windows:

https://sourceforge.net/tracker/?func=detail&atid=542099&aid=3526865&group_id=74815

Just adding that it's whenever the player presses the alt key while turning; repeatedly tapping just causes it repeatedly.

Sidestepping while turning is a major part of Doom; random YouTube video of someone playing Hell Revealed 2 for instance. You can see how often the player in the below video turns while sidestepping.

http://www.youtube.com/watch?v=pyTb4emkHKE

Doom is a very movement focused game, as I’m sure you’ve noticed by all the tweaks that people have requested made to the new movement code in 1.9.x, so that it better matches Vanilla/1.8.x.