[SR-Users] dialplan regex confusion

I'm using the following in dialplan:

id | dpid | pr | match_op | match_exp | match_len | subst_exp | repl_exp | attrs ----+------+----+----------+----------------------------------------+-----------+----------------------------------------------+----------+---------------------------------- 3 | 3 | 0 | 1 | ^30\d{3}#+?1?[2-9]\d{2}[2-9]\d{6}$ | 0 | ^(30\d{3}#)(+?1?)([2-9]\d{2}[2-9]\d{6}$) | \11\3 | normalize prefixed domestic

A R-URI goes in as 30001#12345678910 It comes out as 30001#*\1*12345678910

Can someone help me understand why? I'd expect to be exactly what it was originally but for some reason '\1' is thrown in the middle...

Thanks, Ryan