WPML support for Wiki

One more 'experiment' showed that Wiki stopped supporting 'child' URLs for a wiki subcategory.

In other words,

domain.com/wiki/parent-category/ - works
domain.com/wiki/parent-category/sub-category/ - does NOT work
domain.com/wiki/sub-category/ - works
I've tried to re-save the sub-category - no luck.

Any ideas?