If by "delay" you're referring to the millisecond (not even close to 500ms) flicker, then I would not call that a delay, and it would still be considered instantaneous.

The "delay" is quite normal. mIRC is activating the window (probably by redeclaring it as the foreground child window) which is expected behaviour when dealing with MDI windows. This is normal because you told it to do so by executing the command.

This bug report seems to have changed from /editbox -f to the special case of /editbox -fa, which is quite a different story. You seem to be saying that mIRC can avoid a (insignificant) flicker by checking if the current active window is the one you're switching to. Perhaps.. but so can you:

Code:
if (%window != $active) editbox -f %window


I on the other hand would expect that mIRC insistently and noticably refresh the window when typing /editbox -fa the way it would with any window, otherwise I would be wondering if it did anything at all. Addendum: if I type/execute /editbox -fa (or even editbox -f <window> where window == $active) I expect mIRC to do something noticeable, otherwise I wouldn't type/execute it. In this sense, the flicker seems normal to me.

Again, I'll harp on this point, but if I didn't want the flicker I would make sure I was not activating an already active window. Note that this is the exact same behaviour as /window -a $active, which you are basically saying is also a "bug" by association. I would not agree.