Hello Chris Hayward,
The special symbols are forbidden in 4.3 due to some issues in earlier versions of Sitefinity. However we know of an issue with the fullstop, as you show in your example - if you use it between two strings, the page will generate a 404 error, which prevents you from further editing it.
We have this issue logged in our system for fixing, so you can expect it to be fixed in one of our future releases. Unfortunately there is no workaround for that issue other than removing the periods. We are sorry for the caused inconvenience.
the Telerik team
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