Recently I noticed that, in Rapture, the pan control for Element 3 always seems to be panned hard left, regardless of which program I load (for programs that use 3 or more elements).  I have tried altering it, but it keeps reverting to left. What could be causing this?

First I thought that maybe a control was mapped to this parameter, so I tried running Sonar with controllers tuned off, but this did not make any difference.

After experimenting, I find that the pan control is usually set at the centre position when the program is first loaded, but suddenly pans left after a few playbacks. 

This is very strange!  It's a problem that could easily go unnoticed for a while, so I don't know how long it has been occurring.  It may well be unique to my current setup, which dates from January of this year.  I can't seem to reproduce the problem on my laptop.

Any ideas?

Something to try:  Right-click on E3's Pan control, and see if you have any assignments bound to Rapture's global MIDI Learn.  Reset / clear that assignment under the same right-click menu.  I'm guessing that a CC or aftertouch was inadvertently "learned" to that Pan control, and you have Sonar's MIDI options set to reset on stop (CC1 mod wheel, CC64 sustain, etc.).

b rock

Something to try:  Right-click on E3's Pan control, and see if you have any assignments bound to Rapture's global MIDI Learn.  Reset / clear that assignment under the same right-click menu.  I'm guessing that a CC or aftertouch was inadvertently "learned" to that Pan control, and you have Sonar's MIDI options set to reset on stop (CC1 mod wheel, CC64 sustain, etc.).

That was it.  Problem now solved.

Many thanks.