Occasionally you might notice fonts change within a diagram when you load it. This is especially common when editing a diagram on multiple computers. Most of the fonts that you see in the font list are those installed on the computer that you're working on. If you have been moving between two computers while editing a diagram the change in text fonts could be because the second computer doesn't have the same fonts installed as the first computer and therefore Creately is using the Times New Roman font as a substitute for the missing font.
You can either change your chosen font to one which is common between the two computers or simply edit your diagram on the computer which has the font you need installed.