Having an issue with edge of backdrop being disappeared when frame's size changes

[Layback_]

Hi all,

I should have gone to 'Graphics Help' forum rather than here, 'Lua/XML Help', but I guess this is more like a Lua related issue.

So, I've created a generic Template function for my frames like the following:

function CustomFunc:SetTemplate(whatType, anchor)
    local anchor = anchor or self;
    local backdrop = LSM:Fetch("background", "backdrop");
    local fer12 = LSM:Fetch("border", "fer12");
 
    local template = CreateFrame("Frame", anchor:GetName() .. "Template", self);
    template:SetFrameLevel(self:GetFrameLevel());
 
    if whatType == 1 then -- Extend
        template:SetPoint("TOPLEFT", anchor, "TOPLEFT", -1, 1);
        template:SetPoint("BOTTOMRIGHT", anchor, "BOTTOMRIGHT", 1, -1);
    elseif whatType == 2 then -- Shrink
        template:SetPoint("TOPLEFT", anchor, "TOPLEFT", 1, -1);
        template:SetPoint("BOTTOMRIGHT", anchor, "BOTTOMRIGHT", -1, 1);
    else -- Default
        template:SetAllPoints(anchor);
    end
 
    template:SetBackdrop({
        bgFile = backdrop,
        edgeFile = fer12,
        edgeSize = 2,
    });
    template:SetBackdropColor(0.1, 0.1, 0.1);
    template:SetBackdropBorderColor(0.7, 0.7, 0.7);
 
    anchor.template = template;
end

Then I applied this to frame and resized the that frame.

bar = CreateFrame("StatusBar", "TestBar", UIParent);
bar:SetPoint("CENTER");
bar:SetSize(46, 10);
bar:SetTemplate(1);
 
bar:SetWidth(55); -- Modify width

Since the template frame's size varies based on its anchor points, I thought this would work fine, but as you can see the image below, left & right borders are gone once I changed the width of parent frame, bar.
(Well, they are definitely there, but is not rendered(?) properly)



I also attempted to change those regions' draw layer, but that didn't solve the problem

Could anyone please help me out regarding this?

Thank you!

*EDIT: Applying insets to backdrop didn't do the trick as well.

insets = {
	left = 1,
	right = 1,
	top = 1,
	bottom = 1,
},

**EDIT: Here I've attached those texture files!