If a parameter name is modified in the TemplateData editor, then immediately reverted back to its original value, the TemplateData editor crash when clicking on "Done" :

• the TemplateData editor content is blank and buttons do not do anything, even "cancel" : it's impossible to go back to the page editor
• the modification of the templatedata is lost
• other modification to the template (or it's doc subpage) can be kept on Firefox by reloading the page but are also lost on Edge or Chrome.

Step to reproduce :

1. Edit a template with parameters (eg w:Template:Template sandbox)
2. Click on "Manage TemplateData"
3. If necessary click on "Add 3 suggested parameters" (but the bug is also present on existing params)
4. click on a parameter (named or not)
5. change the name (eg. add a caracter)
6. restore the initial name (by Ctrl+z, paste or manually)
7. click "Done"

Tested on fr.wikipedia and en.wikipedia and test.wikipedia.org on 28/7/2016, connected or not, with Firefox Chrome and Edge, Windows 10 and Ubuntu, all failed.