Why does imgur block images hosted there from being visible on LL?

[Love Space]

imgbox is a good domain for anyone needing to upload their pictures

or even dropbox

[ChaosZen]

I hope nobody minds if I try testing a different image host here. It says they allow adult content, but I've not been able to find any details on user guidelines or limitations. 
 

 

 

...And a test to check direct linking from full size image: