It is strange, but it is not so easy to add Google Static Map links to Facebook. Sometimes it works, sometimes does not. Even worse – the same link being posted several times can show the different results. We faced this behavior in our Places for Facebook mashup where you can describe customized check-ins. The quick search (stackoverflow, developer groups) confirms this problem as well as the lack of reaction from Facebook. Strange.
By the way, check-in messages from Foursquare use map fragment from MS.
I suspect the problem is on Facebook site. If you use some proxy for Google Static Map – it works on Facebook. Proxy lets you include map from your own site. But even with this solution we can see the problem – the map published in status works, the same map being published in check-in record – does not. Is it bug or feature?