Original estimate in planning board get's lost

Original Estimate field get's lost if you create a new version or sub-version, or if changing "Start Date" in GreenHopper's planning board.

Steps to reproduce:

1. Go to GreenHopper's planning board
2. Create a version for your project
3. Set the "Start Date" to some day in the future
4. Create a few issues and a set time estimate for each one
5. Create a sub-version
6. Create an issue to the sub-version, or change the "Start Date"
7. See that parent version "Time Estimate" has changed, it lost it's value and goes to zero. The Original Estimate shouldn't, so you don't loose your original metrics.

There is also another bug with time estimate, please see:

GHS-2466