Latitude D420 - cursor jumps erratically while typing

while typing text, the cursor jumps to a different location (mouse pointer location? like hitting the left button)

additionally, sometimes one or more lines may be selected

if typing fast while this happens, it often causes loss of work (two or three incidents in a row, therefore Ctrl Z is no longer enough to recover the previous situation)

this is a random problem and have not yet been able to identify a condition or interference with other software / hardware


any suggestions?

thanks, alessandro