if it does perform on two different pc's, but only one mouse (is there option to test same model but another mouse?) - then it looks, like the mouse cannot communicate well with the dongle, or the data are delayed into the pc already. You wrote, "it jumps" to another part of text (email for example) - also data has been cached correctly in mouse hardware self - but the insufficient communication or driver (?) delay in pc caused, that it has read all the cached data and processed them at once - also what should happen by scrolling normaly in let's say 0.1 - 0.5 second or smooth enough to scroll nicely, happened instantly - caused "jump efect".
- also it is either bad wroted driver (it cannot handle cached data correctly - for example to emulate smooth slow scroll jump and not quick jump)
- or the communication is distorted and thus it has efect of storing cached data on mouse self because the wireless protocol self throws away data, which are not received correctly - and here originates the delay, until all data about scrolling the roller are received correctly - and when processed in pc immediatelly - it looks like jump
- it can be also hw failure there (mouse and dongle components)
- power issues on dongle ? (usb problem ?) - try to use some usb powered switch and put dongle there
- it can be some delay in OS enviroment self - processing "this" mouse data is slowed down by another process - it has low priority and therefore it is delayed - and after releasing enough resources processed immediatelly with the jump efect...
- it can be there some interference with another wireless device...
it can be also something other You can dream about in point of view of operating system, hardware, wireless communication...
try to change to another piece of hw but same model, try to use the mouse in some other location (outside of the building - in park without or at least minimal another signals coverage), another wireless mouse usage and so one...
try to use the mouse with not scrolling document - but with "zooming" property of some software - for example 3d modeling (try google sketchup free) - and look, if it has same efect - jump change of zoom view ratio - because there can be also synchronisation with the smooth scrolling problem that causes this (it is long lasting problem between smooth scroll and video signal synchronisation) - also video driver comes into play...
it can be anything in between in corellation to wireless communication...
hope I gave U some tips to clear this unlucky situation...
