I updated our WHMCS to v6.3.1 not too long ago and identified an annoying bug when it came to modifying a client product when the service is cPanel based.
The long and short of it is that if you hit "Enter" in any of the fields to submit the form rather than hitting the "Save" button at the bottom it would attempt to sign you into the cPanel of the account rather than saving the form. In some cases the changes were lost and in other times it was just lost productivity due to ending up in a cPanel when you don't need to.
The fix is as simple as inserting the following code:
function getCurrentFileName(){
var pagePathName= window.location.pathname;
return pagePathName.substring(pagePathName.lastIndexOf("/") + 1);
}
if (getCurrentFileName() == "clientsservices.php") {
$('[name="username"]').next().attr('type', 'button');
}
You will insert the code into the "/whmcs/admin/templates/v4/footer.tpl" and the "/whmcs/admin/templates/blend/footer.tpl" files just before the </body> tag.
For more details on the bug and the fix you can see them at http://blog.mddhosting.com/2016/07/running-whmcs-v6-3-simple-fix-may-save-time/
Due to a lack of full templating for the administration area of WHMCS I was forced to use JavaScript to make the necessary change until WHMCS is able to patch this small change into their software.
If you run into any issues or make any modifications do please let me know so I can update the post.