I re-boot daily and just updated the video driver.
I tried those steps you suggested but the corruption is still there but they look different. For instance when 'D' is overlapping 'A' and I move another window over it, 'A' is now overlapping 'D'.
I do not experience display corruption like this in the other editors and IDEs, including Ecilpse, MPLAB, MT4, Notepad2, OpenOfffice, etc, etc..
This might not be related but I mention here in case other members can share similar experiences:
I am using a 2560x1440pixel monitor with DisplayPort and the system font size is set at 125% (my preferred setting).
The Log window in B4A Editor cannot show underscore-characters because text is enlarged but inter-line spacing remains the same.
eg. Log("abc_def") => the text appears in the log as 'abc def' without the underscore.
If I change system font size to 100% (the default), the underscores can be seen but the text corruption problem is still there but less messy.
If AnyWhere Software allows, I would like to install B4A in another PC just to investigate further.