Can this be explained by an extraordinary demand for hedging spot
positions via shorting futures?
The answer to your question is: kind of but there is more to it. Out of curiosity I looked into this a bit after you added the company name. The answer is similar to @will answer above but it was too much to add as an edit, hence, the separate answer.
This stock has went from PLN500/shr down to single digits. Currently trading PLN~8.60. Those numbers are adjusted for a 1:50 split in 2015.
When comparing the current price of a stock to it's future price, you need to adjust spot for dividends and cost of owning the stock (search for Fair Value if an explanation is needed). Owners of this stock have not received a dividend since 2012 and are currently receiving a rebate (not being charged interest) for owning shares--i.e. Short sellers are so sure this stock is going to zero that they are willing to pay an astronomical amount for someone else to buy, hold and loan them shares. That premium for the owner (cost for the short seller) is the difference between spot and future.
This is an instance where market participants are literally saying "I wouldn't buy that stock if you paid me to!"
Though the curve has shifted a bit since your original post, the backwardation is existing because no one has any faith in this company remaining a going concern (at the moment). Oftentimes a backwardated curve can lead to an arbitrage opportunity, however, not in this case. The arb is executed by shorting spot and buying future. For an arb to exist, the current price minus the borrowing cost for a short seller must be greater than the future price--it is not. There is no arb--just a poorly managed company that no one has any faith in.
Anyone interested in the -ve rate being paid to share holders can use this formula (assume the future price = fair value price) and solve for r.