It makes sense that one takes priority regardless of object order. NeoLemmix's object detection basically checks "Is there an object of type A here? If so, handle it. If not, check - is there an object of type B here? If so, handle it. If not, check - is there an object of type C here?" and so on, until every type is checked for.
NL only checks for the individual object, if it's an object type where the individual object matters. So for example - if NL detects "there's a fire object here", the lemming dies - NL never makes any effort to figure out which fire object it is, because this doesn't matter, a fire object will always kill a lemming, so the object order doesn't matter. At the start of the level, NL has already figured out "this pixel is covered by a fire object" and that's all it pays attention to from there on. On the other hand, if NL detects "there's a triggered trap here", NL must then figure out exactly which trap it is (because firstly, it must check the trap isn't already in use, and secondly, it must animate the trap). Only at this point does the order of objects become relevant.