Strange Properties appearing
> Etc, etc. It seems as though it's treating the x in the property title as a variable
No, a property label (or title) doesn't make any arbitrary decisions about part of the character set it represents.
I don't fully understand the issue, maybe it would be good if you try the replicate your issue on [0] so we can attempt to eliminate or identify the potential problem.
I have seen it to appear in [0] and I suspect that this relates to this code {{#arraymap:{{{CentralIndexRef|}}}|,|y|[[CentralIndexRef::y]]}} in your Template:Article
that creates an empty property.
I think if you remove the arraymap call then those arbitrary properties should no longer be created but this isn't really related to smw-core (this parser is provided by SF).
I think the x in CentralIndexRef in combination with arraymap causes this strange appearance, if you would use something else without x the issue might also disappear but again this relates to the use of arraymap and not smw-core.
[0] http://sandbox.semantic-mediawiki.org/w/index.php?title=Special:Properties&limit=51&offset=0
I suspect that entries like CentralIndeB1Ref are empty (when created by the arraymap) and despite being void are still created as property reference hence the visibility in Special:Properties.
[0] https://github.com/SemanticMediaWiki/SemanticMediaWiki/issues/1217