Yongnuo E3-rt/600/canon 600 questions

ok, couldn't find anything on this with a google search so asking! I just snagged a set of YN-600's and the transmitter (e3-rt). Love that it's just like the canon transmitter and I do like the AF assist. But --- here's an odd one.

One of the reasons I snagged them was because I wanted 2nd curtain sync. But...for some odd reason the YN flashes won't fire if the SS is below 2 seconds. My canons synced up nicely and had no issue firing with any SS. But the YN's won't. Wondering if this is just the hard limit on the flash or if there may be a setting I am missing. The manual is of no help, and all i can find for info just states that they can do second curtain sync. LOL, if 2 seconds is the limit, then fine, if I need more than that I have my canon flashes. Just odd that the YN's won't...any help out there?