Relationship bet. UBE section data selection and UBE version data selection

I have two sections in a UBE, a main driver and a conditional section and they both use the same business unit and both have the same data selection.  I have two questions

1. What's the difference between the UBE sections' data selection and the UBE version data selection?
2. In the main driver, I have a header break level on business unit and I use this business unit and call the conditional section. In the initialize section of the conditional section, I append the business unit to the data selection because I want to get all data just for this business unit.  I have two business units but for some reason, only the first one got processed and not the 2nd business unit even though I know the 2nd business unit has data. Is it because both sections use the same business view so it might be the problem?