The Allocation Discrepancy portlet uses the last Time Scale period when displaying data. The weekly detail portlet uses the periods you select in the TSV.
An example is:
We are in week of 8/13 Weekly Detail Allocation Prior week (8/6) = 22 Current week (8/13) = 40
Allocation Discrepancy Portlet set for 1 Period and Weekly Time Scale shows Allocation = 22 (week of 8/6)