Icy Tower 1.5.1, The OS gets slower and slower the more I move the mouse over that window

0.4.14-RC-99-g2671cc4 gcc dbg 4.7.2 linux.
in VBox4.3.12 with VBEMP + inbuilt Mesa.
AC97 driver from rapps.

I can run the game "Icy Tower 1.5.1" quite fine. Especially right after the startup when you have to enter your name, it is still fast.

But as soon as you enter the main menu that changes.
It is still possible to run a game when operating the app exclusively with the keyboard.

But the mouse pointer is horribly slow in the main menu.
And I do have the feeling, that the more I move the mouse, the worse it gets,
up to a point where it is taking literally almost a full minute to open the taskmanager.
Also the keyboard input is starting to lack more and more then.
But If I'd leave the mouse alone, and use just the keyboard, then I can properly play the game, even for extended time.

Expected result
Mouse movement should be fast and no slowdown should occur

Observed result
0.4.14-RC-99-g2671cc4_icyTower1_5_1.webm
0.4.14-RC-99-g2671cc4_icyTower1_5_1.log