Simultaneous XMLHttpRequests using HTMLUnit 2.7

Question

I just updated our HTMLUnit version to 2.7 (from 2.3) and I'm seeing spurious errors in one of my tests. It appears that HTMLUnit is making one XMLHttpRequest at a time, no matter what I do.

Note that this isn't an issue of single-threading the test with with the XMLHttpRequests -- I've confirmed that the test itself continues after I submit the XMLHtppRequest; it just appears that my second request waits for the first to come back.

This prevents the testing of a variety of client/server race conditions, so it's hard to imagine that this is desirable or intended behavior. Has anyone else seen this? Did I miss something? Is there a config option for this?