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Does this mean it was a previously expired domain, with a penalty?
Is it now dangerous for me to link to it from my "good" domains?
mycompany.com is indexed for a long time. No links and such to developmentsite/mycompany.com. But sometimes it shows up in SERPs, and vanishes in most cases an update later.
How come? Don't know - except one suspicion: it's hosted all under one IP. That's the reason, maybe?
albert, that URL sounds like it's been submitted or linked to.
However, a few other people have come to this board and said that the only way that some of their new pages had been included in google was by means of the toolbar. So, instead of looking for complicated theories, I would say that the toolbar helps googlebot finding new pages.