Well, I'm using 4.6 build 4618, and the del key has just stopped working only in phpED. I was playing with the debugger & profiler and EMS SQL Manager analysing PostgreSQL queries to improve speed in a script. The detected that the del key was not working in the Immediate Pane. After ending the debugging session, it was working again. I started another debug session just after, and everything was ok.

Was Del key still working in the editor while it didn't in the immediate?

No, it also stopped working in the editor.

The special thing about this time DEL key stopped working is that I had not to restart phpED to get it back. I tested DEL in a text editor that was already open and all other softwares opened, and the key was ok.

So far, I can't say how to replicate this behaviour.

Please check if key "Delete" is bound to an Editor or IDE action as a shortcut.
Check tools->settings->IDE shortcuts and tools->Settings->editor shortcuts.

Also, please make screenshot of the IDE when you get this problem next time and submit it there.

Only to what it is supposed to be: Editing Commands>Delete

please make screenshot of the IDE when you get this problem next time and submit it there.