In one of our VB6 ActiveX projects we use the DrawText WinAPI call to output strings in a treeview-like grid control. When the user expands a tree node and the vertical scroll bar appears, some artefacts are drawn at the left of the scroll bar. They are not removed if we draw in that area using any WinAPI calls and remain visible until the vertical scroll bar is hidden again:

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As i can judge, these artifacts are some points 'captured' when the scroll bar becomes visible. Here is the enlarged screenshot:

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What is strange is that this happens only for the Segoe UI font. Using other traditional fonts like MS Sans Serif does not have this effect.

What it could be and how to overcome this strange problem?