Including numbers in page name causes 404

[grilledcheesby]

Describe the bug
When creating or editing an Event page, using numbers into the title causes the page to become inaccessible and shows a 404 error.

To Reproduce

1. Create event page and name it "2014-15 Event"
2. Creation is successful
3. Navigating to the page shows 404.

Expected behavior
To be able to see the page

Additional context
Removing the title from the address bar (for example /pages/8 instead of /pages/8.2014-15_Event) navigates to the page correctly. 404 only happens when the first character of a title is a number, numbers work fine at the middle or end of a title

[itinerare]

This a weird one-- but fortunately I was able to confirm that another of my projects (that also includes slugs in some page URLs) doesn't seem to suffer from this problem, so it should just be a matter of "backporting" the setup for handling it to this one.