I'm unable to specify which Steam library I want to install MW3 to

I've got an SSD and HDD in my computer. I don't want to install programs where loading time isn't a big issue onto my SSD so I have a Steam library on the HDD but Steam installed on my SSD.

When I come to install CoD MW3 onto my computer, there is no option to specify which Steam library to install it to.

This is what I should get:

This is what I do get:

I can only assume there is something different about MW3 but I can't imagine what.

Not sure if it makes any difference but I have Black Ops 2 installed on the HDD.

Thanks.