Found a few of options to solve the volume slider issue.
Install aebutton plus or magic button or (as I've done) do a hard reset.
After the reset the volume slider is back to normal, if i restore my device using a backup the problem re-appears. At the moment I've hard reset again and fully charged the battery, turned the radio / phone off to see how long before the battery runs down - so far its been a couple of days and no sudden battery drain so I guess that some of the software I normally install was causing the initial problem.
XDA2 - old faithfull collecting dust.
Mio A701 - now joining old faithfull.
SPV M700 (trinity) - in with the rest
Samsung i900 Omnia - current but about to be changed