Jbresyncthreshold must be a non-negative integer

FreePBX with Asterisk 13

Adaptive Jitter Buffer gives this error
[2016-11-21 18:31:12] WARNING[4655][C-00000024]: chan_iax2.c:1239 jb_warning_output: Resyncing the jb. last_delay 0, this delay -3714, threshold 1000, new offset 3714

so I looked at the help documentation and
Jitter Buffer Resync Threshold supposedly can be set to -1 to disable
but Sip Settings gives an error on save that jbresyncthreshold must be a non-negative integer

is that a bug in Sip Settings or in the documentation?

I’d think it would need a ticket either way.