Hi Mark,
It seems weird to me that you can have two or more copies of an investment (i.e. with same investment file) in the same sub-portfolio. I can't see any benefit to allow that. This only brings multiple same lines in the reports and Portfolio Editor (but not in the investment graphs, where the investment is displayed only once). In addition, the Statistics tab of the Investment Properties dialog doesn't report in this case the multiple instances, which could be considered as a shortcoming. Too, the totals for the sub-portfolio at the bottom of the Portfolio Editor and in the reports might seem wrong if we try to add up the investments. It seems to me that It would be better to allow only one instance of a same investment per sub-portfolio. because leaving this possibility open doesn't seem to be of any interest except for a little confusion.
I usually make a copy of my stock investments to a specific sub-portfolio, and noticed I had made the operation twice, so I had two same instances in the sub portfolio. I think Fund Manager should not make another copy in this case, when one already exists. In the case of an attempted second copy, maybe Fund Manager could do: nothing at all. No action done but no warning message either, because what the user is trying to do is already achieved.
Just an idea.