MacOS 10.13.5 (17F77)
Chrome Version 67.0.3396.99 (Official Build) (64-bit)
Vector skin

Reproduce by:

• Navigate to https://en.wikipedia.org/w/index.php?title=Point_5310&oldid=848093295
• Edit using visual editor
• Insert a Fact template somewhere
• Click the blue "Insert" button
• Switch to source editing
• Immediately switch back to visual, without making any changes.
• Observe that "[[Category:Articles with unsourced statements from {{subst:CURRENTMONTHNAME}} {{subst:CURRENTYEAR}}]][citation needed]" is displayed.

This seems to be completely repeatable.