I have a frequent problem when renaming a file in a lister. I highlight the file and press F2 to open an input box where I can change the name, but the box closes up (preventing input) before I can make my changes. Is there a way to fix this? Can I increase the time that the box stays open for input?
That usually means something else is taking focus just after the edit control opens.
Do you have anything installed that modifies or adds to other program's user interfaces? Or maybe something like an uncommon IME?
I don't have anything else installed that I'm aware of, but it does seem consistent with another program taking focus. I just don't know what it would be. I usually have 4 or 5 DO listers open, if that would make a difference.
Is the same thing happening in any other programs, e.g. File Explorer?
You must have other software installed. It's unlikely Opus is the only program you've ever installed on your computer. 
I don't normally use File Explorer, but I've been using it for renames for the past day. I haven't had the problem occur with File Explorer. It occurs about 25% of the time with DOpus.
I have a lot of programs installed, but I'm not running most of them and I've shut down the one that I thought might affect the renames (FastStone Capture).