Ooh good to know, make sure to add that information to the game page! :)
*edit*
Actually, it only happens when fiddling with the rainy clouds!
I got to the first cloud only making a few small lines and it stopped working just as i made a line to protect myself from the rain.
However i've been able to essentially fill the starting area with lines and still get to that point and further beyond.
*bonus edit*
Actually it looks like there's a cap to the number of lines, but not the length, i've been able to get to the end of the game using just 5 lines (i only released the mouse button to shield from rain)