Joli, masculine before a vowel, 2.14

I am reviewing module 2 and noticed this anomaly (to me anyway as a beginner) about the adjective, joli which is for both masculine and masculine before a vowel. There was no example of a sentence using joli before a masculine vowel noun. It had a example of joli in feminine plural form: "Mes jolies chaussures viennent des États-Unis."

Any explanation would be helpful. 

I am no expert, but all adjectives must match up to the noun they describe, both in terms of gender (masculine vs. feminine) and number (singular vs. plural).  In your example, "chaussures" is plural and "chaussure" is a feminine noun.  So the adjective "joli" adds the "e" to account for the feminine case of the noun, and adds the "s" as the noun is in the plural.
 
If you were to say "my pretty book", it would be "mon joli livre", as "livre" is masculine.  If you were to say "my pretty books", it would be "mes jolis livres".  

I am not quite sure that is the question you were asking, but if so, I hope it helps.
 

If this is the case of beau (masculine), bel (masculine, before vowel), belle (feminine), and why joli doesn't have a separate "second masculine" form, I'd say it's more of the "natural y" liaison sound that is created between i and the subsequent vowel of the next word.

So, when saying "un joli arbre", it already sounds like "zholeeyarbr(eh)", and there isn't a need to create a separate masculine form with its own consonant ending for euphony.

Yes, I know what you mean but in this segment  - 2.14 All About Descriptions (Part 2) the confusing part is that for the adjective of "joli" it said it has 5 forms just as petit and that's what's confusing. 

petit (m) singular, petit (m) before a vowel, petits (m) plural, petite (f), and petites (f) plural [so far so good].

joli (m) singular, joli (m) before a vowel [this is what confused me; the rest of the forms followed petit as above and all good]. How could one have 2 vowels next to each other? That's my question. 
joli enfant? 
joli ami? That's why they use mon amie
joli espagnole?
joli angliaise?

That's all the nouns with a vowel that come to mind. I apologize for my limited vocabulary at this point. 

Sorry torusan,

I finished my reply to Bob-D and got distracted; didn't sent it but by the time I did I saw your response but I'm still confused. My understanding is that y can be a vowel and a consonant. 

Since I can't hear you say it you are saying in your example of the pretty tree it is sounded as:
zho-lee-y-arbr(eh) with the y as a consonant. 

Hmm...if it says there are five forms, then that's an error. There should only be four:

m. s.    joli [Zòli]
m. pl.    jolis
f. s.    jolie
f. pl.    jolies

The pronunciation would be that the 'y' sound is "attached" to arbre (no extra syllable) because of the liaison, i.e. zho-lee-yar-br(eh).

Again, I am not an expert, but there plenty of times two vowels occur next to each other in different words:  For instance:

Tu as-you have
Tu es-you are
Elle a-she has

There are plenty more.  What may be confusing you is the need for an apostrophe when two vowels would have come together.  For instance, one does not say "je ai" (I have), but instead says "j'ai".  But this mainly happens when the last letter of the first word is "e". Now your question might be why is it not "ell'a" instead of "elle a". Not sure I have the answer for you, but I think you sort of get used to it over time.