One thing to check: how have you determined that you and your colleague have the same fonts installed?
I ask because PowerPoint will lie to you about this. If you use, let's say, BozoBold in a presentation, when anyone else opens the file and selects some of your BozoBold text, PowerPoint will show that as the font being used, EVEN IF THE FONT'S NOT INSTALLED on their computer and it's actually substituting some other font.
The best way to check this is to have your colleague close PowerPoint completely, not just close the file, re-start PowerPoint and create a new, blank presentation.
Then have them add a text box, add some text to it, and see if they can set the text's font to whatever font you've used in the "problem" file.
If the font isn't available on the fonts dropdown, that tells you *for certain* that the font's not installed on their computer and if not, that explains why the text spacing is going wonko (forgive the highly technological terminology).