[RPG] Does the “Wild” armor enhancement preserve both bonuses and penalties

You're misusing the guidelines.

First, let's take a look at what the Pathfinder Magic Item Gold Piece Values section has to say on this issue. Turns out, it is specifically addressed.

The correct way to price an item is by comparing its abilities to similar items (see Magic Item Gold Piece Values), and only if there are no similar items should you use the pricing formulas to determine an approximate price for the item. If you discover a loophole that allows an item to have an ability for a much lower price than is given for a comparable item, the GM should require using the price of the item, as that is the standard cost for such an effect. Most of these loopholes stem from trying to get unlimited uses per day of a spell effect from the "command word" or "use-activated or continuous" lines of Table: Estimating Magic Item Gold Piece Values.

Emphasis mine. It then goes on to take Mage Armor as an example of this:

Patrick's wizard wants to create bracers with a continuous mage armor ability, granting the wearer a +4 armor bonus to AC. The formula indicates this would cost 2,000 gp (spell level 1, caster level 1). Jessica reminds him that bracers of armor +4 are priced at 16,000 gp and Patrick's bracers should have that price as well. Patrick agrees, and because he only has 2,000 gp to spend, he decides to spend 1,000 gp of that to craft bracers of armor +1 using the standard bracer prices.

So yes, your Amulet of Mage Armor and Shield is a textbook example of the guidelines gone bad.

This is understandable. The guidelines are famously weak, often breaking with casual use, as you have encountered. This precise case, however, was anticipated and addressed.

This exact question was answered just this Friday in the most recent FAQ posting on paizo's site.

Wild armor and other transforming armor: When I use a wild armor and gain the armor’s benefits, what restrictions, if any, apply to me? In general, when I transform with a polymorph effect and some of my gear melds into the form, what restrictions do I have for melding with large amounts of heavy gear? What about other types of transforming armor?

If you were in medium or heavy load from encumbrance before transforming, you continue to take those penalties in your melded form. Otherwise, ignore the weight of melded items and calculate your encumbrance in your polymorphed form entirely based on non-melded items. When wearing melded armor and shields, if you gain no benefit from the melded armor, you still count as wearing an armor of that type, but you do not suffer its armor check penalty, movement speed reduction, or arcane spell failure chance. If you do gain any benefits (as with the wild property), then you do suffer the armor check penalty, movement speed reduction, and arcane spell failure chance. This also applies to all other situations where you or an armor transform: you always count as wearing an armor of that type, and if you gain any benefit at all from the armor (such as mistmail), you apply the armor check penalty, movement speed reduction, and arcane spell failure chance.

It can be found HERE