Larsen Magnacore Cello Strings Medium

I bought two sets of this strings, one for me and one for my friend. We started playing together on this sets. My set was great, it keeps pitch very well and has nice tone! However my friend was completely unhappy with G and C strings. Both of the strings not keeping pitch. If you press more you can even get to C sharp on C string and G sharp on G which is not nice at all on new strings. After few month it still unchanged. So I don't know what to say. Only idea i have is that thomann sent to us one new set and one old.