There's more than one way to "count" the records. Please describe the method you've used. Otherwise, there's no way to tell you why it's not working the way you expect.
In my layout customers, I have a field called Last_Name_FirstName.
I have a portal which have a field called customer_related::LastName_FirstName_Customers_Related.
To get the right number of customers, I use this summary field : Count of Last_Name_FirstName, Running Count and summarize repetitions to "All Together"
To find the number of customers_related, I use some other field:
I create a calculation field called TotalCustomers_related1 which contains Count (customer_related::Last_Name_FirstName)
I create a summary field called Total_customers_related2 which contains Total of TotalCustomers_related1, Running Count and summarize repetitions to "All Together"
So, in browse mode, everything shows good information. In preview, It calculate only the first record.
In layout mode, double click the layout part label that says header and change this part to "leading grand summary". See if that previews correctly.
Note: your window will scroll differently after this change. If you still want the window to scroll as it did before, (With the first part staying put while the rest scrolls), you'll need to create two layouts, one for browse and one for printing/preview/PDF purposes.
Even with the leading Grand Summary, I still have the incorrect number.
I have something strange. If I Use my two field separately, I have this:
Customers : 4
Customers Total : 5
The calculation field customers total equal Customers + customers_Related.
I could be wrong, but I think the "running count" option is the source of your trouble. Clear that option and see what happens. If this is the only report where you use this field, that option is not needed anyway.