Another thing to add.
If using the remote, cover the viewfinder while metering at it will let stray light in and may affect the exposure settings.
Normally you cover the viewfinder with your face
so it blocks the light out.
If you have the camera in any of the semi-auto modes (Auto, P, Av, Tv etc) and you activate metering/focus/shutter remotely then it might read incorrecly.
Manual metering settings wont be affected obviously.
In live-view it doesnt matter as the mirror is already up.
I dont think there is a mirror lock up on the K-r or K-x (K-5 & K-7 have it). It is in the "drive mode" menu with continous shooting, timer shooting etc.