[BUG] Incorrect matching

[Alex Turbov]

Hello.

I've found a bad bug in sed >=4.2. Trying to match capital letters I
tired this command:

$ echo HelloAfrica | sed 's,\([A-Z]\),_\L\1,g'

expected result: _hello_africa
actual result: _h_e_l_l_o_a_f_r_i_ca

meanwhile., sed 4.1.5 works fine for me!
FYI, my glibc is 2.12.1

please ask me for any requireed information by e-mail.