I'll start up my copy and have a look, I'll reply in a bit.
note: I'm running a non GOG copy off an external HDD.
You are right, there is a delay! I never really noticed it, but now looking for it, I can see how it would be a problem.
It appears to happen when the enemy is a fair distance away, and your character is attacking in melee, or is standing still. There is a pause, before your character runs off to attack.
Shift+LClick walks, but this does not negate the issue.
If you are attacking in melee, and switch to another attack via melee another enemy, I noticed no pause.
If your character is running in any direction, with the aim of just running, not running to attack, and you then tell it to attack something... It appears to pause/delay sometimes, but not others...
In my own games, I've focused a fair bit on using the various combat/magic-arts, than charging head on in. Also, I generally play things slower, so I've not noticed this until it was pointed out.
You're exactly right. I've tried to avoid the problem as much as possible by doing exactly what you said. If you switch to another enemy while the mouse is held down then there is no pause. Before i realized that i would always re-click the next enemy which i'm sure you could imagine would lead to alot of annoyances :)
It's not game-breaking, but yeah it gets a bit fustrating after a while. I just started the game today though and i have to admit the game sucked me right in despite this issue.