I replied to this question on HATT after checking with Adobe.
Tracking changes does not currently work in dropdowns. That's the way it is in RoboHelp 9. Whether you need to submit a bug request or a feature request is up to you.
Please follow this link.
See www.grainge.org for RoboHelp and Authoring tips
Thanks for the answer.
Yes - I posted on Techshoret but got no answer there.
I then posted on HATT and thought that I had got no answer there also - after
checking now I found that of course the one digest mail that I had not read
contained the answer (Sorry!)
I have now submitted a bug request.
A bit frustrating as it is a great feature, but as I use drop-downs a lot then
it is only going to partially help me.