why does this happen?

[quibby_6633]

whenever i use the brush, it just does this, i cant explain what it does (watch video for example)

[kglad]

check your bottom-most option.  what is that?

[n. tilcheff]

This is a well-known Flash 8 bug: you can't draw inside flipped symbols.

Unflip it externally or open it for editing not 'in place'.