WebDynpro and system definition

I have a query on creating a system for webdynpro - this comes out of a very strange problem we had with a dropdown list box on a web dynpro screen.

We have a portal with its own WAS/Java (ad do most development systems). We have a backend R/3 which is currently a 4.6 release.

The WD (WebDynpro) is developed and deployed to the portal and runs fine for everything except for the drop down box - it has the values but will not disply the list (we know it has the values as we can select the box and scroll the values using the arrow keys).

We have fixed the problem but want to know WHY...

Basically the WAS sytem has the info for getting both the meta and data from the R/3 system (jco destinations). Rally thats all we needed to do. Eveything else on the WD works fine .. Ie text returned from the R/3 system is displayed.etc etc.

We changed the system the iview was pointing to from pointing to the R/3 system to pointing to the Portal/WAS. But this means that we would have two system entries in the users personalise / user mapping for the end users to keep up to date. - is this correct?