"Unexpected item in the bagging area". And then again, "unexpected item in the bagging area."

It's a chant that drills down into your brain. It invades your dreams in the dead of the night, turning them into frustrating nightmares.

I should know how to handle a self serve checkout. I've been swiping tins of tuna and weighing tomatoes for a decade now.

But recently, things have unexpectedly got a whole lot worse. That chant has become louder, has been repeated more times and that red light to attract attention has flashed ever more brightly.

And in the process, my fruit and veg has found itself bagless, spending far too much time hanging around with the grime and muck of a bagging area.

It's the unexpected consequence of the plastic bag ban. The situation would be so simple to solve it, so why isn't it?

What's changed?

Prior to the bag ban, more often that not, I used the single use plastic bags provided. Which I would reuse. For something. At some point. Scout's honour.

Now, dutifully, I bring my own bags. Usually a rag tag collection of worse-for-wear carrier bags and so-called green bags.

And here is where it's all falling down.

You see, in these bags I bring from home, I might throw in a book for the bus ride; there might be a pen, or four, at the bottom. On the way to the supermarket I might pick up some greens from the grocer. Maybe some lunch.

After I've been around the aisles, I put my basket on one side of the self-serve and bags on the other. I go to swipe the first item. And all hell breaks loose. Chants and lights assault me. I am electronically berated for having an "unexpected item in the bagging area".

It's actually that book, or those pens, or the onions from next door. But as far as the super sensitive bagging area is concerned, which knows the weight of every item you've purchased, I may as well have snuck a half kilo of rump into my reusable.

So then comes the wait for a member of staff, currently occupied explaining to a shopper why, no, they can't have a miniature toy because they have to spend over $30 and $28.50 just isn't enough.

And then when they do come over, you get a glance of suspicion as your bags are rifled through to ensure there isn't a surreptitious un-scanned Milky Way hiding at the bottom.

"You know your bags have to be empty when you pack them?" I'm helpfully told.

"I get that, but where am I going to put the various detritus that I've been carrying around for the last hour?" I reply.

"Maybe put your bags on the floor and stack your items in the bagging area instead?" you're not helpfully told.

So I do. And soon an unstable mountain of groceries is lying next to the checkout in the bagging areas which is sans actual bag.

A cucumber balancing on top of some lemons, ready at any moment to make a dive for the shop floor. Even if it stays in the bagging area, it's perilously close to a discarded tissue, left by a previous shopper, stained worryingly red. Could be beetroot. Could be blood. Who knows? But my tomatoes are inching inextricably towards the abandoned, grimy Kleenex with every item I pile on top.

I have another reason why it's annoying. Sometimes I split my transactions between two cards — stuff for me, stuff for home. The result is this same — half full bags upsetting the electronics.

From my experience, it seems Coles are more prescriptive at turning on the bag scales. In Woolworths having semi-full bags hasn't been a problem. Plonk them in the bagging area, fill them up, and haul away. Not an angry alert in sight.

It suggests Woolies have weighed this all up and decided, in some stores, the lesser of two evils is to wear a bit of shoplifting so as not to annoy customers with half full bags.

Coles and Woolies are a bit cagey about all of this. Neither would say how many stores turned on or off their bag scales and the reasons why. I get it, you hardly want to flag the store where, if you are cunning enough, you could scan one tin of soup rather than two and get away with it.

Woolies said: "Many of our customers keep personal items in a separate bag and use only empty bags in the bag racks area".

Over at Coles, they said "weight scales can assist customers with their payment by ensuring they don't accidentally scan their items twice". Which is a point. They also said their staff were there to "lend a hand" to struggling customers like me, laden down with bags.

But how about this? When you put your bags, containing a few items, in the bagging area, you can reset the scales to zero. And, from then on, it can weigh each item with gay abandon. This seems to not be an option.

I know, I know. It's a first world issue. I could plan my shopping trip better. But like Liberal MPs and their leaders, it's the little things that build up and potentially result in you swapping shopping horses.

If I hear, "unexpected item in the bagging area" I might just do exactly that.