RUNNING_AVG() is a table calculation and can be computed in various ways: Table-down, table-accross, or cell. The values you get may be different, and the default computation may be different depending on how you build your dashboard (i.e. in what order you drag dimensions and measures to it).
Click on "Edit table calculation" and see what of these options is selected. My guess is that if you select "Table down", you would get the number that you see without the week dimension, but to be absolutely sure, I would need to look at your data.
Please play with the settings above and see if this helps you clarify your issue. If not, please provide a sample of your data, and I'll be happy to look at it.