I don't know will this be fixed because C2 is almost retired and this is more or less annoying "feature" rather than a bug.
When grid size is changed from top bar "view" option, it has to be visible (double click to keep it visible), otherwise grid size won't work after clicking to layout or toggling grid size -option to off/on.
Steps to reproduce.
1) click click view -option on top.
2) change grid size (height, width).
3) click "show grid" -option OR click on layout.
4) only 1 grid size value changed is applied.
How to change grid size properly:
1) double-click view -option on top, so it will stay visible.
2) change grid size (height, width).
3) toggle "show grid" -option off/on OR click on layout.
4) both grid size values are properly applied.
Tested in Construct r279 & r259 (both 64-bits) running Windows 10.
capx: h*t*t*p*s://www.dropbox.com/s/3je7lvy1g3of7hp/grid%20size.capx?dl=0
(remove * -symbols from https to make link to work properly)