I think you've changed the toc.ncx items the wrong way round, i.e. you've changed blue to match red instead of red to match blue. If it's easier to remember change the upper <content> item to match the lower <content> item and leave the lower item alone.
Taking 'Part 1' as an example, after the edit both the 'Part 1' and 'Chapter 1' should look like
Code:
<content src="SMem2utf8_split_003.htm"/>
You will need to re-do the ZIP to EPUB conversion first, so you've got a fresh toc.ncx.