While the European Central Bank has gobbled up eurozone bonds, another group of investors has dumped them at a much faster clip, hastening the recent sell-off in the region’s bond market.

Certain computer-driven hedge funds built up large bets that bond prices would rise after the ECB announced its quantitative-easing program in January, data from Royal Bank of Scotland show. The funds, known as commodity trading advisers, then quickly sold their bond holdings in late April as the market turned.