merge sequence about "background"

[sunnylost]

csso version: 3.1.1

I have this css file:

div > a {
    background      : url("about:blank");
    background-size : 100%;
}

.demo > a {
    background-size : 100%;
}

this will generate:

div > a {
    background : url(about:blank)
}

.demo > a, div > a {
    background-size : 100%
}

looks good, but when i swap these tow declarations position,

.demo > a {
    background-size : 100%;
}

div > a {
    background      : url("about:blank");
    background-size : 100%;
}

i got this:

.demo > a, div > a {
    background-size : 100%
}

div > a {
    background : url(about:blank)
}

div > a's background-position would be reseted to its initial value. I know background is a sooooo complicated property, but is this a bug? I have this habit that set background and background-size at the same time, the reason was for compatible with old IE.

[lahmatiy]

Yep, it's a bug. Duplicates #143