functions.php child file overwriting

Hi everyone.
I hope some of you could help me because i have been looking and i couldnt find any solution.
The thing is that im creating a personal website (in local) with u-designe theme. Them i created a child theme. So, the problem is that when im navigating arround the web is everything ok. But when i get into the wortpress panel to change something, my child functions.php is overwrited and feed with all the parent functions.php functions. And then i get an error about redefined functions.
I have try somethings:
1) If i remove functions.php child file, its works well. No problem.
2) If i leave the file empty, it gets overwrited again.
3) If i leave the functions that i have programe still the same problem.

Any idea?,
Ill be really thankful, this is driving me crazy.
Cheers.