Hi Colin,
Don't know what the problem is but here's a guess:
The BPMN add-in used ShapeScripts to draw elements. Perhaps the scripts are dictating the fonts used in these elements, while the 'normal' drawing engine (or whatever) is doing so for any other text (diagram notes, non-BPMN stuff, etc.).
The BPMN add-in provides some pretty good examples of how ShapeScripts handle things. Still, within the BPMN scripts there are no examples of how fonts themselves are handled - I just checked them all again to be sure. The ShapeScript documentation is still 'out of date and incomplete' according to Sparx, though they are actively working on getting it up to speed, and I have every hope that this will be done soon (before or by 6.5, which I anticipate soon).
--- Neil: any update on this?
You could always try creating a sample shape of your own using the script from one of the BPMN elements (one with text) as your starting point. Try experimenting with some kind of SetFont or PreferredFont command (or SetFontSize or whatever) to see if you get anything (at all) that works. A good indicator would be to see if the keyword changes colour in the editor when you finish typing it. But note that not all valid keywords do this (for example, some of those used in BPMN bezier curves are not coloured in the editor, but the shapes appear to draw just fine - don't know if this is an error or not).
I know that's very hit and miss, but it could be a lot less work than recreating a whole lot of BPMN elements - they are so position-sensitive!.
[Remember this is a guess, and treat this with an appropriate measure of seasoning; work on a backup project at the very least.]
BTW, if you stumble on anything, via the above or otherwise, please update this thread. I must soon dive into some BPMN work, as well as other ShapeScript oriented stuff, and any info I can get is bound to save me some time and hair (and I have so little of either these days).
Good hunting,
David