I'm waiting for the answer of
help@kobobooks.com but I notice another thing which could explain certain bugs during the selection of the word to look for in the dictionary: in spite of a very fact gap between the lines, it is possible to "click" (=tap and hold) between the line of the above and the one below and therefore to find yourself without any selected word ...
Also having a Glo, I do not encounter the problem and I think it may be related either to the resolution of the Aura HD (and more recent models ?) or simply to the fact that the screen being smaller, it is more difficult to click between 2 lines. What do you think about my idea? Have you the same problem?