After we use a jetpack the game stop playing footstep sounds for a while. If we use a jetpack for a long time it will take several time walking to hear the footstep sound again, reloading the save will make the footstep sound work again until you fly with jetpack.
Single player commands used to have a similar bug when using the "fly" command and they fixed, the pegasus from mo'creatures also does not cause this bug, the only mod that is causing footstep sound bug now is industrial craft 2. Please fix this, this bug is really annoying. If others coders could fix you can fix too.
Unfortunately there's nothing reported in the log.
If you want I can send a video, but I think it's not necessary...