When I try my demo in Firefox 6 everything disappears when you do anything related to going left, which is when Construct flips the sprite to face the opposite horizontal direction. Haven't tried on any other computer so it could be a problem my end. Anyway here's the demo:
Cave
I'm using the latest version r51.2! <img src="smileys/smiley1.gif" border="0" align="middle">
Anyway if this is known about then sorry! <img src="smileys/smiley5.gif" border="0" align="middle">