Odd issue after upgrade from Apex 4.2 to Apex 5.1

I've been working on an Apex 4.2 application for over a year now.

Last week i bit the bullet and upgraded to Apex 5.1 and am working through a few issues.

I'm generally i'm liking the new Apex editor but the current issue is a bit odd.

On pages where i have radio groups, the label text is shown twice before the radio group.

I've attached a screenshot to show - above the line is the actual screenshot in Firefox 43.0.1 and below the line is the output from firebug.

It clearly shows there is a <label>..</label> tag containing Encrypt All (id=P6_ENCRYPT_LABEL below) but there is also a <legend>..</legend> tag (the blue highlighted line) with a class u-VisuallyHidden which also containst the same label.