It is probably related to the way markdown works. For instance, by putting an asterisk between square brackets (like the bullet entry code in bbcode)
[*] you get this
If you type three consecutive underscores,
___
You get a horizontal rule (same as the hr tag in html)

But if you have more than one checked box in a group
[*] this is
[*] not good
the markdown sees the consecutive asterisks and it becomes a weird mess.
But, at least you can [-]^[-] take a nap.