I thought I was crazier than usual when I was trying to fix a control alignment problem in AltInventory when I realized it wasn't me this time (or at least not all me). It turns out, the ItemControl is rendering Backpack items with a three pixel border but if the same exact item is moved to the vault and then set to the ItemControl, it is rendered without the border, causing the item contol to look misaligned.
In the image below, both items are stacks of Exceptional Leather. The one on the left is in the backpack, the one on the right was in the Vault.

The code for this example is:
Code:
import "Turbine";
import "Turbine.UI";
import "Turbine.UI.Lotro";
localplayer=Turbine.Gameplay.LocalPlayer.GetInstance();
backpack=localplayer:GetBackpack();
item1=backpack:GetItem(1);
vault=localplayer:GetVault();
if vault:IsAvailable() then
item2=vault:GetItem(1);
end
testwindow=Turbine.UI.Lotro.Window();
testwindow:SetSize(240,140);
testwindow:SetText("Item Test");
label1=Turbine.UI.Label();
label1:SetSize(100,20);
label1:SetPosition(10,45);
label1:SetTextAlignment(Turbine.UI.ContentAlignment.MiddleRight);
label1:SetText("Backpack");
label1:SetParent(testwindow)
label2=Turbine.UI.Label();
label2:SetSize(90,20);
label2:SetPosition(120,45);
label2:SetTextAlignment(Turbine.UI.ContentAlignment.MiddleLeft);
label2:SetText("Vault");
label2:SetParent(testwindow)
backdrop1=Turbine.UI.Control()
backdrop1:SetParent(testwindow)
backdrop1:SetSize(35,35)
backdrop1:SetPosition(80,65)
backdrop1:SetBackColor(Turbine.UI.Color(.2,.2,.2))
testitem1=Turbine.UI.Lotro.ItemControl();
testitem1:SetParent(testwindow);
testitem1:SetPosition(80,65);
testitem1:SetItem(item1);
backdrop2=Turbine.UI.Control()
backdrop2:SetParent(testwindow)
backdrop2:SetSize(35,35)
backdrop2:SetPosition(120,65)
backdrop2:SetBackColor(Turbine.UI.Color(.2,.2,.2))
testitem2=Turbine.UI.Lotro.ItemControl();
testitem2:SetParent(testwindow);
testitem2:SetPosition(120,65);
testitem2:SetItem(item2);
testwindow:SetVisible(true);
This example assumes you have an item in the first slot of your backpack and an item in your vault.
EDIT: As expected, Shared Storage items work exactly like Vault items, that is, they render without a border