fputs/puts dangerous (in C)?

Question

I've been having trouble with fputs lately: when printing some strings in a text file with fputs, it happens I get other characters than A-Z, a-z, 0-9 in (chars that aren't part of the string). I made absolutely sure the strings all end with the null character. Unfortunately I can't give you more information, since I did not personally test the program, that was the feedback I received. But after I replaced fputs with fprintf it worked properly.

So my question is: is fputs sort of dangerous? Have you ever had trouble with it?