My WA#7-program had two mistakes:
1) The output information about bloggers should have the same order as in the input. I.e. for sample test the answer

_denplusplus_
1:
2: strange_human, xoposhiy
3:

xoposhiy
1: _denplusplus_, strange_human
2: strange_human
3: strange_human

strange_human
1: _denplusplus_, xoposhiy
2: xoposhiy
3: xoposhiy

is wrong. By the way, there's nothing said about it in the problem!
But when I corrected this mistake I still had WA#7.

2) Wrong output: in several cases a comma was outputed before first name in list. Just a stupid mistake :) After correcting it I got AC.

3
c
<blog><friend>a</friend><friend>d</friend></blog>
d
<blog><friend>a</friend></blog>
a
<blog><friend>a</friend></blog>

Answer
c
1: a, d
2:
3:

d
1: a
2: c
3:

a
1:
2: c, d
3:

My WA7 didn't pass this test:

3
xoposhiy
<blog>
Tomorrow I found <friend>_denplusplus_</friend> to
 be smartest blogger in the net.
Also I received interesting link from
 <friend>strange_human</friend>
</blog>
_denplusplus_
<blog>
Some shit about my work.
<friend>xoposhiy</friend>
</blog>
strange_human
<blog>
<friend>xoposhiy</friend>
<friend>_denplusplus_</friend>
</blog>

I didn't sorted third lists. Correct answer:

xoposhiy
1: _denplusplus_, strange_human
2: _denplusplus_, strange_human
3: _denplusplus_, strange_human

_denplusplus_
1: xoposhiy
2: strange_human, xoposhiy
3: xoposhiy

strange_human
1: _denplusplus_, xoposhiy
2: xoposhiy
3: xoposhiy