Darkbasic Classic is an interpreted language, which will always be slower than pure machine code. Darkbasic Pro uses compiled code, but neither of the two are very optimised.
One of the most important aspects of speed is your own code though, if it's badly coded, it will obviously never be fast. For 2D, and if you're using DBP, I recommend you look into the Lock Backbuffer (I think that's the command) command which will let you write to the backbuffer which is faster than writing directly to the screen. Try and minimise function calls as they take time, and try to get rid of unnecessary code.
Its not a bug, its a feature!