thomaskilian / sargasso - thanks for your responses. In answer to your requests:
725 being an old build - yes, agreed. We have rather a convaluted process for adding software onto the network where I work, so we only tend to get upgrades when things go out of support, rather than being on he front foot. For the purposes of this thread, I think it is safe to assume that we'll be stuck with that build for the forseeable future.

Step-By-Step explanation of what I am doing - sure. Here goes.
1. I have set up a new stereotype (in the configuration menu - Configuration->UML->Stereotypes) of 'impact' for the object element. We have applied this to all the items we want to tag.
2. I have then set up the tags I want to use (again using the configuration menu - Configuration->UML->Tagged Values) and in the notes field below the title and description, I have used the syntax I found on page 102 of the manual (e.g. for a list of values, I have used the Type=Enum; Values=Val1,Val2,Val3;Default=Val2;).
3. I then create a new instance of the 'object' element, stereotype it as an 'impact' and then navigate to the tags field on the properties tab to start adding my tags. The tag names I have created are all visible in the top dropdown (entitled 'tag'), but the dropdown entitled 'value' below remains blank and does not appear to bear any relation to the restrictions I have placed in the tag notes.
Can you see where I am going wrong thomaskilian?