Tool Palette previews show incorrectly

The block previews show correctly in Designcentre, but when I add them to a tool palette, some of the previews look as if they have been created while
zoomed out.
I've tried recreating the blocks, zooming to extents and purging, before saving. There is no other elements in the drawing file and the preview is correct in Designcentre and the file open dialog, but still incorrect in the tool palette! I've also tried, as suggested in the help files, to update the tool's preview image by remapping the block source path.
I'm working in Autocad 2005 with servicepack 1 loaded.
Please help?
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