This is more a bug-fix request, rather than a feature request. But because I was told by the support that the way it works now is by design, I'm creating this feature request :) The current behavior is, to put it mildly, quite unhappy.
If there are made some changes to test parameters and then confirmed by Enter key, the Test Parameters dialog is immediately closed, but the modified values are not saved! I think it's quite annoying.
The only way, how to save changed parameters is by using [Tab] key, before pressing [Enter] key, or directly by clicking [OK] button. Simply, using Enter is natural and I believe preferred way, to confirm changes, unless the input element is a multi-line input.