sub() function do'nt alter string length in awk 3.1.5

[Frantisek Hanzlik]

Hello,
I not know when it is my mistake or gawk bug - in simple example below
I delete some chars from string variable, and after this string is
modified, but its length is unchanged.

awk 'BEGIN{A="1234567890abcdef";
 for (i=1;i<6;i++){print length(A),"A=" A ".";sub("....","",A)}
}'
16 A=1234567890abcdef.
16 A=567890abcdef.
16 A=90abcdef.
16 A=cdef.
16 A=.

When I use gensub() instead of sub(), result is as I expected:

awk 'BEGIN{A="1234567890abcdef";
 for (i=1;i<6;i++){print length(A),"A=" A ".";A=gensub("....","",1,A)}
}'
16 A=1234567890abcdef.
12 A=567890abcdef.
8 A=90abcdef.
4 A=cdef.
0 A=.

OS/GAWK versions:
- GNU/Linux kernel 2.6.16-1.2122_FC5 #1 i686, Fedora Core 5 distro
- glibc-2.4-8
- GNU Awk 3.1.5

Yours sincerely
Frantisek Hanzlík

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