If you create a property page and then delete it, it will still show up in the pages Special:Properties and Special:UnusedProperties - it shouldn't. And similarly, it shouldn't be returned by smwfGetStore()->getPropertiesSpecial() or smwfGetStore()->getUnusedPropertiesSpecial(); though I assume that's related.
By the way, it's strange that Special:Properties now lists unused properties as well, but that might be on purpose, so I don't know if it's a bug.
Version: unspecified
Severity: normal
Probably this bug 18406 is somehow related to this too.
I also think that unused properties with a datatype declaration should only be on Special:UnusedProperties.
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