iBooks and 'define' delay

Since I upgraded to iOS7 my iBooks have been messed up in regards to the define feature. On my iPad 3 it takes 2-3 full seconds to look up a word. With the previous OS it was instant.

I've noticed that my iPhone 5 is slightly better when looking up words in iBooks, but it has some delay too.

What's up with this? The define feature works fine in Safari (iPad 3) without any delay.

/confused