VDC hi-res graphics.

Hello,

I am new here, so let me introduce myself before I post my problem:

I am 46, programmer at work, electronics and retro-computing hobbyist at home.
Wife, kids, mortgage, problems, yada, yada...
So the hobby is my venting outlet.
Nice to meet you all.

Now to more interesting stuff:

I started to explore VDC graphics programming on C128.
I am reading Compute's  C128 Programmer's Guide and researching online while learning VDC programming.

I have been able to draw hi-res pixel by pixel graphics using 80-col chip, but after I return from graphics to text, my leftmost column in text mode is invisible.
I must hit RUNSTOP/RESTORE to recover proper 80-col display.
My C128's VDC has 16 kB of RAM.

This BASIC program reproduces the issue:

10 fast:ad=dec("cdcc")
20 sys ad,128,25:rem turn on graphics, turn off attributes
30 rem do something here, clean the screen, draw pixels etc.
70 getkey a$:sys ad,64,25:sys 65378:end:rem turn off graph., turn on attr., restore characters from rom

Do any of you guys have any idea what am I doing wrong?

Thanks!

---
Marek