Strange tick mark in Preview

When I tick a checkbox in a fillable PDF in Preview, there is a strange double tick symbol. It's like a tick with a cross on it. How can I have a correct tick/check symbol ?

I'm on El Capitan 10.11.5 with Preview 8.1 and the problem came with any fillable PDF with a checkbox

Someone else asked this here: https://discussions.apple.com/thread/6754677?start=0&tstart=0

The answer given was "It seem [sic] Preview in OS X has a capability of making a normal PDF (non-editable) editable and I'm guessing that it's doubling up on top of the editable symbol that's already in your editable PDF. I had the same problem and I was making my PDF editable with Adobe Acrobat Pro. I fixed the issue by changing the appearance setting in properties for the checkbox."