Comment 5 for bug 1653893

Reproduced with 0.91 r13725, 0.92 r15299 on OS X 10.7.5

Workaround if you have 0.91 still installed:
1) open document in Inkscape 0.91
2) open Document Properties > Grids
3) for Spacing X, Spacing Y:
use the arrows for each entry to "nudge" the value (one click on the 'up' arrow, one on the 'down' arrow, so that the result is still 1.00000 px)
4) save drawing, quit Inkscape 0.91
5) open drawing in Inkscape 0.92
--> grid is correctly scaled
Repeat step 3 for Origin X, Origin Y if needed.

If you don't have Inkscape 0.91 installed anymore:
1) open document in Inkscape 0.92
2) open Document Properties > Grids
3) for Spacing X, Spacing Y:
multiply each current entry ('1.00000') with 96.0/90.0 = 1.06666667

The underlying issue is that user units for grid settings don't work well with default grids (because the specific settings are pulled from the preferences, and not from the SVG file). The steps described for Inkscape 0.91 will cause the explicit settings to be stored in the SVG file, and then properly adjusted to the document drawing scale as expected in Inkscape 0.92.