Today, at last I found another way to do this.
On the group that you specified the page break, in the properties window, expand the Group
section.
See Pagination in Reporting Services (Report Builder and SSRS)
You can set the BreakLocation property in the Tablix Properties,
Rectangle Properties, or Group Properties dialog boxes, but you must
set the Disabled, ResetPageNumber, and PageName properties in the
Report Builder Properties pane.
You should see a PageName
field. This field can be set to that of one of the field data values from the dataset used by the tablix.
Once you have set the PageName
field, you can add a textbox to the Page Header/Footer and set the expression to use the PageName
field. Built-in Globals and Users References (Report Builder and SSRS)
=Globals!PageName
This should then change on each group change, and be visible on each page.
I have realy struggled finding a good solution for this, so if I need to clear up the answer, please feel free to suggest this.