MacDraw II does not support tabs. (Tabs are treated as spaces.) MacDraw Pro supports true text tabs. When opening a MacDraw II document in MacDraw Pro, tabs are converted to spaces. This is done so that the character spacing will remain the same.
However, when saving a MacDraw Pro document as a MacDraw II file, tabs are not converted to spaces. The tab characters remain in the text blocks. Since MacDraw II treats the tab as a space, tabs will cause only a single space to appear at the tab.
MacDraw Pro users should create their documents accordingly. If the user knows that they are creating the document for MacDraw II users, they should not space text with tabs, as this feature is not supported. (Of course, this goes for any other feature that MacDraw II doesn't support, such as gradients, most colors, etc.)