In facing pages, applying a discretionary hyphen —either pressing Command+Shift+- or applying a keyboard shortcut— it evolves a pattern when it is applied to the last hyphenated word in the spread:
a) if the discretionary hyphen is applied in an even page it is rightly applied.
b) if the discretionary hyphen is applied in an odd page immediately the next step is that you are sent to the next spread, with three effects:
Must it be reported as a bug?
It certainly sounds like a bug, but you haven't mentioned the version of ID, so I can't test here.
In all Mac versions as far as I remember,