Floated element floats into post content in IE, Safari, and Chrome

UPDATE: Added a second alternative to match the targeting currently defined by your parent theme.

Try adding:

// generic target (first answer)
a.more-link {
    display: block;
}

// more precise target based on parent theme (second answer)
.entry-content .more-link { 
    display: block;
}

Note sure that will get you to 100% across all of your target browsers but it’s a good start and I’m happy to assist further if it creates additional display issues for you.