Graphic problem

I am new to Blitz Plus after upgrading from Blitz Basic.
I am having a problem running simple programs.
When I run the following program I just get a Black window (Blitzcc)
No graphics are drawn.
The only way I can get it to draw the graphics is to click the Blitz Debugger TAB, and then the BLitzcc Tab.
The graphics then draw correctly.

This is a sample Program supplied with Blitz Plus that exhibits the problem :-

; Line example
Graphics 800,600,16
; Wait for ESC to hit
While Not KeyHit(1)
; Set a random color
Color Rnd(255),Rnd(255),Rnd(255)
; Draw a random line
Line Rnd(800),Rnd(600),Rnd(800),Rnd(600)
Wend

Any ideas what I am doing wrong.

TIA

Andy

; Line example 
Graphics 800,600,16 
; Wait for ESC to hit 
While Not KeyHit(1) 
cls ; <-- you forgot this
; Set a random color 
Color Rnd(255),Rnd(255),Rnd(255) 
; Draw a random line 
Line Rnd(800),Rnd(600),Rnd(800),Rnd(600) 
Flip ; <-- and this
Wend

It is also good to get into the habit of setting the buffer to backbuffer before you begin your program... just add the line "Setbuffer Backbuffer()" before you're main loop.

I have finally found the 'Bug'
The program I am writing uses a Window Canvas.
When the program was starting up, if the mouse pointer did not touch the canvas screen area, it would not initialise the graphics.
I was really pulling my hair out over this (What I have left!)
I fixed it by setting an initial mouse position on the Canvas screen using the mousemove command.
I know all you experienced programmers will be rolling your eyes, but it might help another Newbie!

Andy