The following is a recent example of the user experience with the 2017 source editor that just happened to me when following normal Wikipedia administration procedures:
- Open Wikipedia:Requested moves#Requesting technical moves to list a new request.
- Following the process instructions, copy the template code listed in that section.
- Move to the Uncontroversial technical requests subsection and enter the Edit source mode.
- Paste the template code and fill in the fields
- Press the Save button. Then press the Preview button.
- Find out that the final page shows the template code, not the evaluated template.
- Remember that you are supposed to press Ctrl+Shift+V every time you're working with anything other than plain text, or it will do random things.
- Close the Preview view.
- Delete the <nowiki> tags.
- Preview again. Find out that the template now evaluates, but produces an error.
- Scratch my head wondering what the hell may have happened this time.
- Copy the template code again below the previous one, this time without any formatting magic, to compare the expected result with what the previous paste created.
- Realize that the previous paste also had inserted italics code ('') around the identifiers for page names in the template. (Surely editors will expect format to be kept from the original page, right?)
- Remove the italics code, and the second copy of the template.
- Preview the page and find out that it finally does what it should have done three minutes earlier.
- Save the page.
- Uninstall the source editor in disgust.
I posted it at the previous bug report, but I'm not sure that those are being taken seriously. The comments there by prominent developers give the appearance that they're disregarding real users feedback on lieu of some mythical Visual Editor user who may or may not want to paste text with format in the source editor.