I don't think it's a bug..... The ships are waiting to off load..... Also, once refinery quota in near by systems is reached, they pace of the refineries is slowed as is your income from those refineries!!!!!!! It's one of those things were you've delepted the source and ships no longer need to go there......... So, once your reached refinery qouta.... Schuttle the refineries and gets credits unless u don't need it!!!
A good tactic, build refineries as early as possible b/c u may need those resources longer into the game..... in my 8 hour game i've played so far, i've reached the quota at a lot of gw and can schuttle these refineries. I've built 800 in this game and 70% of my systems have reached there limit....
Take a look at my ss of them.. http://www.xfire.com/screenshots/zpm/?ss_file=f081fe7a6b1d3a36104d1670021ca6d640088f78.png
not to mention my credits available....... 800000, 262000, 114000 wow...