The camera is pointing in the wrong direction while the level is loading.
In some themes the ice blocks don't use a texture directly, but rather it is generated dynamically by a shader. The Egypt and Artic themes are like this, for example. There are other themes that do use a normal texture. Check if the problem occurs in all themes or if it is only in some. On another note, I have checked the memory leak you mentioned and indeed memory is constantly being lost while playing the levels. It seems to be a problem with some UI particle effects. I have been able to fix it...
Big technical problem starting with Ice World
In the next version, 0.3, the new Magnet block will have that property, preventing jumping (apart from attracting the ball if it makes contact with the tractor beam). Although I don't rule out that in the future there will be a block exclusively dedicated to preventing jumping. Maybe a glue block or something similar.
A new brick/block idea is not something incredibly strange.