Unwanted color change

Corel Draw X6 - The document converts automaticaly all objects (inluding text) from c0 m0 y0 k100 to c72 m58 y53 k79. No matter how many times I set black back to 100 and the rest to 0 when i open the document all black colors are again in the cmyk mix. If you try to convert back to k100 using the find and replace comand it says the document can't find that color. What can i do???