I tried deactivating each plugin, same problems.
Details: the header starts to load correctly, without the small icons. The menu bar displays OK. Then the menu bar gains about 12px in height, placeholders appear where the icons should be and finally, a white border shows up around the menu items.
All this happens with the search box disabled. If I activate the search box, it shows up under the menu items, and the menu bar grows to twice its normal height.