$input is not always modal. This is the entire premise of this bug post and discussion. Currently, $input is modeless when called from a dialog unless you pass 'u'-- but 'u' should not activate modality (not according to the description of its behaviour, anyway). You should probably re-read the link I sent above that explains what "modal" means, because I'm not sure you're on the same page with what modality is.
I know what modal means, I made several tests and they showed that $input is modal in most cases (I thought all cases).
I also didn't say the u switch should activate modality, just that it's what is happening (in most cases and regardless of the u switch) and that I want that behavior avalaible (modal $input).
The point is that if you're relying on behaviour that is a side-effect of a feature and not the feature itself, we should correct the side-effect. In this case that would mean changing how 'u' activates modal $inputs when called from a custom dialog, and then creating another properly named switch that does only one thing: force a modal $input (or potentially force a modeless $input).
I agree with this.
Carefully re-read my last post[...]