[Plugin: W3 Total Cache] Combined JS loads twice, one gets cancelled?

Ive been noticing something weird about the way some of my pages load. The combined JavaScript gets two requests and the first one gets canceled. It looks like this is taking a couple of milli seconds away from my rendering time. Here’s a couple of example, from two pages. Please note item 3 and 4:

http://www.webpagetest.org/result/101201_16T8/1/details/

http://www.webpagetest.org/result/101201_16TS/1/details/

When you scroll down to request headers it gives the same information for both JS load attempts so they’re definitely the same JS script. Why would W3 cancel the JS one time and only on second attempt load it correctly? Is this something I need to be concerned about? I do want my site to load as fast as possible, obviously. Thanks!