Moving down while shielding makes switching weapons not work. However, ONLY if you use WASD for movement, and use the space bar for switching weapons. If you replace those with any alternative, it's fine (such as using the mouse scroll instead, or using the mouse to move instead). I use the default controls except moved shield to Left Shift. Since I usually play using those controls that cause it to not work, it's annoying when trying to switch weapons while trying to block attacks (since I often switch while shielding). Is anyone else having this issue? Since I know a lot of people play using different controls, could someone test to see if this bug happens while meeting the same conditions?
Switching weapons does not work under a certain condition
Except that it works perfectly when I do something such as W+D+Shift+Space, but not S+Shift+Space. It's not a cheap keyboard, at least not as cheap as the one I had a month ago, where that combination of buttons worked fine. I can't remember if it worked on this keyboard or not at one point, that's why I'm asking other people to try it themselves, in case it's some very strange bug in a recent update (not the one today though, it's happened before that)
It's your keyboard's design. Keyboards don't provide a distinct wire for each of the buttons to the keyboard chip, because that's just way too much wiring. The chip doesn't have that much pins to be connected to.
Even a not-cheap one like Logitech G510:
http://www.logitech.com/en-us/gaming/mice-keyboard-combos/gaming-keyboar...
Allows only 5 buttons at a time (feature named Multi-key input)
Remapping shield away from shift/ctrl/alt may help.
You have a cheap keyboard that can't handle all the buttons being pressed at the same time. Some keystrokes get lost which is why high APM games need gaming keyboards.