List of steps to reproduce (step by step, including full links if applicable):

• Go to https://en.wikipedia.org/w/index.php?title=Wikipedia:Sandbox&action=edit
• Replace input with:

'''they see me ''rollin''', they hatin''''

fo real, '''they see me ''rollin''', they hatin''''

'''they see me ''rollin''', they hatin''''

• Press preview.

What happens?:
'they see me rollin, they hatin'

fo real, they see me rollin', they hatin'

'they see me rollin, they hatin'

What should have happened instead?:
they see me rollin', they hatin'

fo real, they see me rollin', they hatin'

they see me rollin', they hatin'

Actually I'd expect "they see me rollin', they hatin'" (italicized single quote in rollin'), but wikitext codes are ambiguous so who knows what was intended. (using HTML would be recommendable when that matters)