I saw this sentence in the current issue of Lomás TV's newsletter.
A Pedro lo mandé traer un litro de leche.
I had to look at it twice to understand why the lo was not le.
At first glance traer un litro de leche appears to be a noun clause used as the direct object of the verb.
That would make Pedro the i.o. and le would be correct.
I ordered a liter of milk be brought for Pedro.
Incorrect, of course, since that interpretation would have required a <
They translate the sentence in the article which makes the use of lo more easliy understood.
I told Pedro to bring a liter of milk.
Pedro still appears to be the i.o. in their translation but apparently using the infinitive (traer) rather than a noun clause (que...) makes all the difference.
I just found it interesting how the double verb construction changed the part of speech of the object pronoun from that of a verb+noun clause construction.
I know...too much time on my hands!