Inverted adjective in "in matters political"

Solution 1:

While done much less often in English than some other languages, such inversions are used for emphasis. Here the 'matter' is more important and the fact that it is a 'political matter' is less important. Try removing the adjective and see if it significantly alters the meaning. In this case the second 'political' only adds a bit more clarity.

We use these constructs sparingly, but in both conversation and writing. If it had been worded as you expected, it would've been understood the same, because we tend to emphasize the subject, verb and object and place less emphasis on prepositional phrases and their objects.

Solution 2:

While you can analyse this as an inversion, I think there is another analysis which has some attraction: as a condensed relative clause.

So

matters political

is an abbreviation of

matters which are political