Bonds issued by governments was as a stable investment symbol for many years. But can thing change? Of course, all world is changing all the time only most of the times we are too stubborn to notice those changes. The key of changes is that a person does not change that fast as environment is changing. New people are coming always to the markets and they are changing the attitude to many things.
Now has come the time when the attitude to government bonds also is changing. Financial markets are never stable and there aren't now. Because all the debts of governments that are huge finally are bringing some consequences. Everything has its limits and debt of a government has those limits too. When limits are breached bad things happen to these countries. The Greece was first example of many that are waiting in the future among developed economies.
The thing about high debt is that when liabilities are too high it makes look the issuer as unstable one and that makes to increase borrowing costs. High borrowing costs together with high debt make interest payments as huge and no country can afford it for long period. You may check for interest conditions on financial portal Bloomberg.
The more country has financial liabilities the more problems it is facing. The another thing that politicians have not enough will to change the situation when it is really bad because unpopular decisions are needed and nobody wants to do those unpopular decisions to bring fiscal deficit in balance. That makes investment in governmental bonds quite risky investments and it is no a symbol of the safest investment tool.
However, it is strange that some investment funds or pension funds are still allowed to invest only government bonds which is completely meaningless at these days realities...