FreeCamera Jumps into air when back pressed while looking at ground

Hi,

i don't know whether is this is a bug or not (or)i don't know whether other people experienced this behavior .

when i press and hold back button while looking at ground the frecamera jumps into air and slowly it drops down.

for example: take flat2009 look at ground

.

Click and hold back button camera jump sand touches the roof after that the camera start dropping slowly.