Hi Rich
Silly question but it's nothing to do with yout tube choice is it? And are you moving at the time?
think this can happen if your moving and you select the wrong tubes well it has for me at least!
When you put the the position keeper on I take it you have id the target taken the first bearing and height measurement input that then waited a while to take the second bearing and measurement then worked out course input that then the AOB then taken a final height measurement then switched on position keeper?
Theres a couple of good instructional videos on the bag of tricks thread that help. Made a toatal hash of manual targetting the first times I used it - don't worry you wil get it
Hope this helps, still early morning here so not totally awake!
Steve