While the broader market for Swiss stocks has risen modestly this year, one ‘entity’ has outperformed its peers by such a staggering margin, it has left bamboozled market experts struggling for an explanation.

And that company is…the Swiss National Bank.

The price of a share in Swiss National Bank in August rose above 3,000 francs ($3,143) for the first time, more than double the level of a year ago, and up 50% since mid-July, as the Financial Times noted in a story about its performance.

Shares of the SNB trade like any other company listed on the Swiss stock exchange, though because of their price liquidity is somewhat thinner. The Swiss cantons together own 45% of the SNB while 15% is owned by cantonal banks and the remaining 40% by private individuals or companies. The Swiss Federal Government owns no shares.

Given the SNB’s holdings – it has demonstrated a voracious appetite for Apple stock and currently holds more than $80 billion in US stocks – the shareholder-backed hedge fund is also having one hell of a year. Perhaps it’s understandable that shareholders see these gains as a driver of value.

And of course, the Financial Timeshas a few theories about what’s been driving the bank’s astounding gains.

One is that, because of the bank’s stellar P&L, it will almost certainly make a dividend payment this year (it has occasionally failed to do so, like in 2015). Dividend payments are fixed by law at a maximum of 15 Swiss francs per share.

If paid in full, that would amount to a yield of 50 basis points – far superior to the minus 15 basis-point yield on the country’s 10-year bond.

Another is that some German investing newsletter issued what amounts to a “buy” call:

“German investor newsletter Actien Börse encouraged a buying spurt after likening the shares in July to ultra-rare “Blue Mauritius” 19th century postage stamps. Trading in the 100,000 SNB shares is thin, so even modest buying or selling leads to significant price swings.”