This is because in Kate the tab key indents instead of inserting a tab character. If your indentation width is smaller than tab width, Kate inserts spaces. If indentation width is larger than tab width, indentation is done with a combination of tabs and spaces.
You get the desired behaviour if you set the tab width to the same as the indentation width.
I agree that this is very confusing. One should be able to set 'indent with tabs' and indentation width would then be determined by tab width.
This is because in Kate the tab key indents instead of inserting a tab character. If your indentation width is smaller than tab width, Kate inserts spaces. If indentation width is larger than tab width, indentation is done with a combination of tabs and spaces.
You get the desired behaviour if you set the tab width to the same as the indentation width.
I agree that this is very confusing. One should be able to set 'indent with tabs' and indentation width would then be determined by tab width.