I had the same issue, with the ghost shooter game, and with the game I made following that tutorial.
Quite frequently the player movement (controlled with the arrow keys) gets stuck in one direction.
For example, I'm moving to the left by pressing the left arrow key; once I lift my finger from the key, the character/player sprite continues to move to the left until it gets to the edge of the game space. Moving in any other direction does not work, and the only way to regain control of the character is to press the left arrow key again (or the down arrow key if the character is stuck going down, and so on).
I have tried to recreate this myself, but it seems so random.
I'm using Windows 7 - 64 bits.
Graphics card is Nvidia GeForce 8800
My browser is Chrome.
Using Construct 2 - R52