The results showed designer doodles differed from their purebred parents in just over half of all comparisons.
Researchers looked at problem behaviour such as a fear of traffic or loud noises, separation-related issues or excitability.
They found that in 82% of cases where one parent would display some problem behaviour, their doodle offspring were likely to show a more exaggerated version of that behaviour.
Some owners reported finding it extremely difficult to train their dog or impossible to leave their dog alone.
The study said that as the cocker spaniel, for instance, was designed to flush out game from dense areas of woodland and grassland, the dogs were bred to have high energy, mental resilience and intelligence, which could be “more of a problem in pet homes”.
It added that when a cocker spaniel was bred with a poodle, those characteristics – combined with them having smaller crossbred offspring – could result in more problem behaviour.
Dr Rowena Packer, senior lecturer in companion animal behaviour and welfare science at the RVC and senior author of the paper, said: “These aren’t the kind of behaviours we want to ignore. They’re not benign.
“Preconceived beliefs, such as the idea that designer crossbreeds are naturally easy to train or are safe with children, can have serious consequences if they aren’t supported by evidence.”
The study also found differences between the owners of crossbreed and purebred dogs.
Crossbreed owners were more likely to be first-time dog owners and more likely to use non-professional sources of training advice, such as social media or friends and family.
