This is a known, old, issue from the earlier days of Live (and SoD on my current computer) when playing in EQW windowed mode. At least a few years ago, no fix was available for it. (And, since it is minor, I have never complained about this one.)
Just a "hey, I also have this issue."
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In the event someone knows of a fix:
a. Pentium 4, 3.2 Ghz
b. ATI Radeon x600 256 MB AGP (Catalyst 9.3 drivers)
c. 4 GB (2x2 GB of ram)
d. Win XP Home, 32 bit (Mostly fully patched)
e. DX 9.0c
f. 1280x1024 resolution, Windows and "In Game"
g. SoD running in requested directory
h. Error occurs with single or duel logins from the same directory
i. No spell graphics, environmental effects, or targeting ring on as options (If curious, the npc name flashing is what I use)
j. SoD GUI setup with 5 chat windows, error usually affects OOC and Auction in the window provided for this text, but has been found in my "Guild" window as well.
h. SoD is "bound to single processor" (to eliminate any potential hyperthreaded processor issues)
i. SoD played with EQW from SoD