When the ownership of the property is in doubt. When an owner’s true claim of title is questionable and may be challenged. One as to the validity of which there exists some doubt, either as to matter of fact or of law; one which invites or exposes the party holding it to litigation. Distinguished from a “marketable” title, which is of such a character that the courts will compel its acceptance by a purchaser who has agreed to buy the property or has bid it in at public sale. Herman v. Soiners, 158 Pa. 424, 27 Atl. 1050, 38 Am. St Rep. 851.