Oh yes. Quite a few. http://spanish.about.com/od/nouns/a/double_gendered.htm
Why is the correct spanish sentence not: "Ella oye a la radio en la mañana"? Where "a" should serve as "to". I would think so as other sentences have reported: "veo a" or "oyen a". Thank you!
I think the a you are thinking of actually has nothing to do with the verb, but is actually what it called a 'personal a'. It is used in sentences to indicate if a person (or sometimes animal) is the direct object or the subject of a sentence.
EX. Veo las fresas (I see the strawberries) - the 'personal a' is not needed
Veo a la mujer (I see the woman) - the 'personal a' is needed to indicate 'la mujer' as the direct object.
With oír, "Él oye a la niña"(He hears the girl) and "Él oye una flauta" (He hears the flute)
The quick answer is never, but its not quite that simple.
The sentence, A él le gustan las fresas", will translate into English as, He likes the strawberries*. In this case, "a" comes before our subject "He (él)", but this is only because in Spanish this sentence is structured differently. While in English "He" is the subject (He likes the strawberries), in the Spanish sentence "él" is actually the indirect object (loosely translated "The strawberries are likable to him).
"Gustar" is a reverse construction verb. In "A él le gustan las fresas", "las fresas" is the subject and "le" is the indirect object while "a él" provides more clarification on "le" (it could also be "a ella"; in cases such as "a mi me gusta", "a mi" provides emphasis on "me"). In English, it would be the other way around with "he" as the subject and "the strawberries" as the object. Even so, I wouldn't say that "a" is used to indicate the subject of a sentence. I think it's clear once someone understands the reverse construction verb that, as in the example given, "las fresas" is the subject and "le" is the object. I think that stating something even slightly incorrect in a grammar explanation will only lead to much more confusion later on.
Simply because "a" translates as "to" in some cases doesn't mean that this preposition is always used in the same way as "to" is in English. For example, "escucho música" means "I listen to music". My grammar reference has more detailed explanations as well as a list of what "a" is used for, but I haven't read it yet. From a quick glance at it though, it doesn't seem that "hears/listens to the radio" falls under any of the uses of "a".
Radio was short for << la radiofonía >> years ago. It therefore follows the normal feminine rule because it is an an abbreviation for a noun which had an "a" at the end and is feminine... :-) Another example is << la moto >> because it comes from "la motocicleta", or << la foto >> from "la fotografía". I am told there are many more....
You see that the sentence has (...en la mañana) This implies that it is in THE morning because of the singular 'la'. The Spanish phrase would be, "Ella oye la radio en las mañanas." You see that by adding an 's' to 'la' and 'mañana' makes it the plural, "mornings". I hope this helped.