

Then make sure pango is not using graphite pango module by deleting /usr/lib/pango/1.6.0/module-files.d/pango-graphite.modules.

The word chosen for testing is thingyam (သင်္ကြန်) as rendering involves re-ordering. In mymr-pangomod implementation, re-ordering is totally taking care by pango module and Masterpiece Uni Sans opentype font doesn't have any rule for re-ordering (there's no opentype feature for re-ordering, pls correct me :-) So if rendering is not using pango, it won't be shown correctly.
Firstly, preferrred alias for sans-serif family is set to Masterpiece Uni Sans family.

Typing thingyam (သင်္ကြန်) in gedit with ibus-waitzar results the following-

Rendering in gedit is correct and rendering in candidate window is wrong; no re-ordering takes place.
Secondly, preferrred alias for sans-serif family is set to Padauk family.

Below is the result-

Rendering in gedit is wrong as expected since pango is not using graphite module and surprisingly rendering in candidate list is correct !!! But it's confirmed that candidate window is not using pango for rendering.