In the attached project (created with ProjectLibre and anonymized for this issue test), the cost rate table B of the resource "P" is set to 3.20 as Cost Per Use. That cost rate of the resource "P" is used twice: in the tasks on rows 9 and 13, which should result in the total cost of the resource "P" of 6.40 (i.e. twice the cost per use). Yet the RBS shows the cost of "P" as 3.20 instead (see attached screenshot).
The cost of "P" in the RBS changes to the correct value of 6.40 if one resets the Percent Complete of the affected tasks 9 and 13 to 0%, and returns to the incorrect value of 3.20 if the tasks are set to 100% again.
I haven't been able reproduce the issue with a simple newly created project and so adapted an existing one where the issue was originally observed.
projectlibre-1.6.2.zip (used without installation)
java version "1.7.0_101"
OpenJDK Runtime Environment (IcedTea 2.6.6) (7u101-2.6.6-0ubuntu0.14.04.1)
OpenJDK 64-Bit Server VM (build 24.95-b01, mixed mode)
The issue persists in the current projectlibre-1.7.0.zip (running as non-admin user, without installation) on Ubuntu 17.04 Mate, 64-bit.
openjdk version "1.8.0_131"
OpenJDK Runtime Environment (build 1.8.0_131-8u131-b11-2ubuntu1.17.04.3-b11)
OpenJDK 64-Bit Server VM (build 25.131-b11, mixed mode)