"When will GM finally pay us back?"

It's a question I hear a lot from readers who are concerned about the effects of GM's 2009 bailout.

Many are surprised to hear that General Motors (NYSE:GM) already has paid back its bailout loans from the U.S. government.

GM has completely satisfied the terms of the deals it made with the U.S. Treasury back in 2009. There's nothing left for GM to do. But that doesn't mean that taxpayers have been paid back.

In fact, they haven't -- and they might not ever be paid in full. Here's why.

GM has done its share, but taxpayers are still in the hole

GM received a total of $49.5 billion from the U.S. government as part of its "bailout." That money funded GM's high-speed bankruptcy proceeding and allowed the company to get back on its feet once it had exited bankruptcy in mid-2009.

That $49.5 billion was a loan, and under the terms of that loan, GM agreed to pay it back with a mix of cash and stock – stock in the "new GM" that was created during the bankruptcy proceeding and given to the government at that time.

GM has complied with those terms. In fact, the company repaid its debt years ahead of schedule. But as you'll see in a minute, there's a problem: GM's stock price isn't high enough to repay the full $49.5 billion.

That means that the U.S. Treasury, which is in the process of selling off its remaining GM stock holdings, is going to come up short once all of those sales are completed. How short? Read on.

A breakdown of GM's repayment to date

Of that $49.5 billion that was lent to GM, the U.S. Treasury has so far recovered about $35.4 billion. Here's how it breaks down:

GM paid back $6.7 billion in cash, the last of which was paid in April 2010. That was when then-CEO Ed Whitacre declared in TV ads that GM's debt had been "paid in full." (I bet he wishes now that he hadn't said that.)

$13 billion via GM's IPO, back in 2010. GM didn't actually get any money from its own IPO – it was done primarily in order to let the government sell off part of its holdings. The Treasury Department sold about 45% of its total GM stock holdings in the IPO.

The U.S. received another $2.1 billion when GM bought back some preferred stock from the Treasury in late 2010.

The U.S. got another $5.5 billion when GM bought back 200 million shares of its stock from the Treasury last December. At the time, GM and the Treasury agreed that Treasury would sell its remaining holdings gradually, on the open market.

Treasury has received about $8.1 billion from its sales of GM stock on the open market since the beginning of 2013.

That leaves about $14.1 billion of the $49.5 billion loan still unpaid, and the Treasury Department with about 113 million shares of GM stock left to sell.

To break even, Treasury would have to get about $125 per share for its remaining shares. But GM's stock is currently trading around $36. At current prices, the Treasury's remaining stock is worth a little over $4 billion.

You see the problem.

When all is said and done, we'll be out about $10 billion

Unless GM's share price suddenly takes off in a big way, Treasury is likely to come up about $10 billion short once it sells off its remaining GM stock.

What happens then?

Legally speaking, nothing has to happen. As I said, GM already satisfied the terms of the deal.

Now, we could argue that GM might have a moral obligation to make taxpayers whole. GM does have a lot of cash on hand, as a reserve against the next big recession.

Of course, as an investor, I need to point out that holding a big cash hoard is a smart move by GM's new management. Handing a big chunk of it over to the government isn't really a prudent idea from the perspective of keeping GM's finances strong.

On the other hand, we could argue that a deal is a deal, and GM lived up to its end. We might also argue that the $10 billion "investment" by the U.S. government got a good return in other ways, by saving tens of thousands of American jobs, and the American economy is better off when GM and its Detroit rivals are healthy and profitable.

What do you think? Is GM obliged to do something here? Scroll down to leave a comment and let me know.