Can you upload a test case?
And what version are you using?
Version: 39.0.2256.48 - Opera is up to date
Update stream: Stable
System: Arch Linux (x86_64; Deepin)
I'm not sure what do you mean by test cast, but here is an example of a simple php file in my local server.
<form action="" method="post">
<input type="text" name="name" value="">
<input type="submit" name="name" value="Submit">
When I open it in the browser and press tab to move to the submit button the page crashes!!!