I'm on my third MS wireless mouse/ keyboard combo- the first two were optical - this new one is laser. The first two had all the symptons that you describe- mainly, I think , due to lack of range, even though the sender/ receivers are only a foot or two away from each other.
Anyway, I picked up the phone, and got onto MS Tech- they just kept upgrading me with no quibbles. Good service, other than the opticles should have been better in the first place.
Anyone want a couple of MS keyboard combos, that don't work well? MS told me to keep them!
PS- Another optical cordless mouse that I purchase a year ago for my laptop has perfomed faultlessly!