Should moving a milestone to a series retarget the blueprints to that series?

This is related to my earlier solved question at https://answers.launchpad.net/launchpad/+question/77221

Here's the sequence of events prior to the problem described in that question:

1. I targeted a number of blueprints to series 2.9
2. I created milestones and targeted some of the blueprints to those milestones
3. I later decided to eliminate series 2.9 and moved the milestones to trunk

My assumption (which I neglected to check) was that moving a milestone from one series to another would
retarget anything targeted to that milestone to to the new series if it was previously targeted to the old series.

I'm making this a question rather than a bug because I'm not sure how this is intended to work.

Charlie