Well, since it will constantly cycle through all the events in the Event Editor, the previous code is going to keep getting executed as long as the conditions set for it still apply. While the mouse button is down, what happens according to the code is this:
At 19, it sees that there's 1 Marker and 1 Center of marker, so Player turns to face the Marker, begins moving, then turns to face the Center( having it turn to face the Marker is actually unnecessary, since afterward it's immediately turned to face the Center in that same line of code, and also because the Marker and the Center have the same coordinates anyway).
At 26, it sees that the mouse button is down, so Player turns to face the Cursor. Keep in mind that no time has passed since Event 19, FAIAP. I'm not exactly sure how it decided that this particular direction change would take priority if it tried to make Player look at both the Center of marker and the Cursor, but that's what happens whenever the mouse button is down.
Now once the button is up again, the condition for event 26 is false, but event 19's conditions are still true. So from then on it points the Player at the Center of marker, until Player reaches it and triggers the event that destroys the Marker and its Center.
So it looks like what you need is a way to test how long the mouse button was held down for. If there's just a short click, a target is created and the player moves to it until it reaches it. If the button is pressed for longer than that, the player should instead follow the cursor for as long as the button is held. Here's what I did:
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Hope this helps! 