It is just that. Link can never set the item, which is disabled by dMap data, for use with the button.
Link should still set the disabled item (just not use it).
I suggest you put a check box labeled "Disabled items can still be set to buttons" in the Disable tab within dMap data.
In general, having Link be unable to select it is preferable. Perfectly implemented (which dmap disabled items are, regrettably, very far from), that would be pretty much what you'd need to have multiple characters (one item would have no properties except a Link tile mod and would be disabled on every dmap but the one on which you are that character). It also lets you grant all sort of situational items that may be in the same item class as standard issue items, etc.