Create a new InDesign Layout (8-10 Pages)
Go to Master Page -> Create a Text Frame ->
Go to Type -> Insert Special Characters -> Markers -> Section Marker
Duplicate the Section Marker to Left & Right Page on a Master Page
On Page 1, Go to Layout -> Numbering & Section Options -> Section Marker
Insert a Section Marker, e.g. SECTION A on Page 1
Notice that on your page 1 the Preview of word SECTION A did not appear immediately.
But if you press cmd + option + shift + y (Overprint Preview), Page Preview will automatically update the current page with the correct preview of the Word SECTION A.
But if you turn off (Overprint Preview) the section marker also disappear from the view.
However this only affect the 1st Page of the Document, because in the 2nd to next succeeding Page you can clearly see that the section marker appears correctly.
If you want your Section Marker to appear permanently, you have to SAVE and Close your document and re-open it.
Now, if you save and close the document and you decide to change the section marker for ex. From Section A to Section B, yet the Preview will not immediately update to correct section Marker. It still display the old Section Preview Name on Page 1 but not on Page 2 to next pages.
Once again you have to Save and Close the Document to update it correctly.
I don’t know if all InDesign CC 2015 is affected or I’m the only one experiencing this Bug.
I think it is only a screen redraw problem. It should be correct if you click twice W (not being in text tool mode).
There is a known screen bug problem in InDesign CC 2015. Hopefully, there will be an update before long.
I think Wilhelm's workaround is the answer.