Steps to reproduce:

• Open the TemplateData editor for a template doc page.
• Close the dialog.
• Edit the template, adding a reference to a new parameter like {{{foo|}}}.
• Open the TemplateData editor dialog again.

The new parameter will be missing from "add suggested parameter". This is caused by aggressively caching the expensive scan for parameters. One solution is to hash the text or otherwise test that the cached parameter list still corresponds to the text.