Can't see the borderlayout with flex settings and <separator/> after zk6.5.1

Steps to Reproduce

I found this issue when reviewing test case B50-3327522.zul
or use https://zkfiddle.org/sample/2s357og/2-can-t-see-the-borderlayout-after-zk6-5-1
it works fine before zk6.5.1

Current Result

the width of borderlayout become 0

Expected Result

a visible borderlayout

Workaround

remove the hflex="1" and vflex="1" of borderlayout
or remove all <separator/>