Comp Plan change resets Interval to Date Sales achievement

We have situations where employees switch comp plans mid-month. For example:
Employee# 123   Comp Plan A    01-JUL-13 to 15-JUL-13
Employee# 123   Comp Plan B    16-JUL-13 to 31-JUL-13

This comp plan change causes salesrep's Interval to Date (ITD) Sales achievement to be split up across the 2 comp plans.

Also, there is a scenario when Employee goes on Leave of Absence (LOA) and returns from Leave within the same month. OIC generates a new srp_plan_assign_id for the employee even though employee's old and new comp plan are the same. For example:

Employee# 456   Plan A   01-JUL-13 to 15-JUL-13
Employee# 456   LOA      16-JUL-13 to 25-JUL-13