Mike Christie at en.wp reports that when performing the sequence:

1. copy template,
2. paste template,
3. edit parameter of pasted template,
4. paste template

Step 4 pastes the template with the parameter values added in step 3 not the original ones.

"To reproduce:

1 Edit [[User:Mike Christie/Sandbox3]] in VE.
2 Select the 13 C (produced with {{chem|13|C}} ) in the middle using the mouse; make sure to select some text on either side, since pasting a template doesn't work unless it's embedded in a string. The colons are there to make it easy to be sure you've got some text in addition to the template.
3 Copy the selected text and then paste it at the end of the sentence.
4 Click on the pasted template, click on the jigsaw piece, and change the 13 in parameter 1 to a 15. Apply changes.
5 Now paste again at the end of the sentence. You'll see that the pasted template contains a 15, not a 13; so the copy/paste buffer was modified by the edit to the pasted template."

Another test case using a different template:

1. Edit https://en.wikipedia.org/w/index.php?title=User:Thryduulf/sandbox&oldid=566402676#Section_3:_tl.2C_etc_templates_added_in_VE in VE
2. select "tlp: {{tlp|as of|1999}} :" and copy it to the clipboard
3. paste the template elsewhere.
4. edit the template you have just pasted (change parameter 2 to 2013) and apply the changes.
5. paste the template again.

Expected result: tlp: {{tlp|as of|1999}} :
Actual result: tlp: {{tlp|as of|2013}} :

Interestingly, pasting into a text editor gives the 1999 value as originally copied, not the 2013 value you get pasting into VE.

Version: unspecified
Severity: major
See Also:
https://bugzilla.wikimedia.org/show_bug.cgi?id=49396