I was minding my own business when suddenly my opponents neighboring planets jumped from 15 influence to 500 influence.  I looked and they had three solar nexus with influence com online.  (which, btw - is a stupid to have such a huge and sudden bump)   So I purchased the nexus from them in diplomacy.  
Next turn I looked forward to seeing my influence surge ridiculously.  But alas - it did not.   Nor did their influence drop.  WTF?  I checked and sure enough they were still getting the nexus bonus.   I decommissioned the nexus and that is finally when their influence dropped back to 12.  

Is this a flaw or a feature?  Because it certainly sucks.