Was it intended for the first clicking area to require you just to hover your mouse above it for it to work, or was it meant for you to actually click first?
After finally noticing the option to hold on the alternate trade for a list of all different items that hero will buy, I've noticed something: when just clicking on the item to swap, you need the amount of energy +1, or else you can't swap; but if you go into the list of items, you can swap with any item for the exact amount of energy. For example, if I want to switch to an axe using just the basic, I would need 3 energy, but if I use the list and select the same axe, i only need 2.
Thanks for the bug report, we'll have our QA team look further into this to confirm. Please note that for all future bug reports, please use either our ticketing system at http://cloudcade.helpshift.com or alternatively, by posting it on our Bugs sub-forum at http://forum.shopheroesgame.com
*Autoclicker included.