To clarify this for future users (and because this question often causes problems and confusion), please use the method I have described above to set up your multichannel sequence correctly for export.
Then if your delivery details specify “mono tracks”, export as follows:
In the Audio tab specify the total number of outputs you require.
And select Mono for the Channel Layout.
The export will consist of “mono” channels.
If you require channels with their correct source labels (typically 5.1 on channels 1-6 and stereo on track 7-8) you can select these explicitly in the export menu. Click the plus sign to add a stereo pair (having made sure that it has been routed to 7-8 in your mixer).*

Premiere’s routing options are very flexible but you have to have the patience to understand how they work and how to set up your sequence and your source tracks correctly.
* I have unintentionally shown the L/C/R/Ls/Rs/Lfe 5.1 routing here but usually these days you will be asked for L/R/C/Lfe/Ls/Rs (which you can of course choose from the dropdown menu).
Simon Ubsdell
hawaiki