We strictly use Fibonacci story point values by the book. When the development team is working on an issue we encourage them to break it down into smaller pieces for their work and to give a more granular burn-down but without impacting the committed-to volume of the agreed whole. Presently the clone function is used for this but then further tweaking is required to adjust the story points of the clones and original issue. This causes some noise on the burndown chart and in the respective reports this looks like lots of scope change events but it isn't - it's scope neutral. Also the clones don't inherit the original's workflow state of, in our case, "commissioned".
We would very much appreciate the possibility of a "split" function, which would provide a dialog box to enter a summary for each of the new issues, inclusive of the original. It should also be possible to enter directly in that dialog the Story Points which each of the new issues, including the original, should have. This must total the same as the story points of the original. On pressing OK, the new issues would be created and the original adjusted in its summary and story point value. All issues created should automatically have the same state and assignee (as well as other meta data such as components, labels, sprint etc.) as the original did prior to the split. All of this should be registered as a single split action on the reports and be completely invisible on the burndown chart.