Mont. Code Ann. § 25-7-602

When any cause is tried and submitted upon a written statement of facts agreed to by the parties or their attorneys, such statement shall have the effect of a special verdict or finding of facts and judgment shall be pronounced thereon as upon a special verdict or finding of facts. In such case, no finding of facts shall be made unless such statement shall fail to embrace all the facts proved and in issue, in which case any additional fact may be found upon evidence which is not repugnant to the agreed statement.