In CRM Online 2015 Update 1 instances I experience charts on forms not showing the correct data until they are manually refreshed.
Charts in general show all data from the underlying view when the form is loaded. Only after manually refreshing a certain chart does it show "Only Related Records". As an example, I have added a chart to the Account entity as seen below. Both the chart and the shown subgrid are using the same view. Even though there is only 1 related record the chart shows all data from "My Open Opportunities" after form load:
After refreshing the chart by clicking the small recycle-icon the correct data related to the current record (in this case 1) is shown:
I have tested this in 3 different CRM Online 2015 Update 1 instances which all exhibit the same behavior. Additionally, this is seen for both system and custom entities. A similar chart setup in CRM Online 2015 without Update 1 works as expected.
This issue is supposed to be fixed in Service Update 1 for Microsoft Dynamics CRM Online 7.1.1. From the changelog: "Charts within a subgrid are displaying all records when they should actually display only related records.".
The expected release date is around the middle of December.