In answer to this recent post on the old GPlates-discuss mailing list, where only parts (blocks) of a high-res exported numerical raster were getting exported…
…this was a bug in GPlates which is fixed now (and will be available in GPlates 2.3). It happened to numerical (floating-point) rasters, but not colour rasters, and only for quite high resolutions.
There were actually a few related bugs such as exporting sufficiently high-resolution regional rasters, or viewing them in the 2D map projections with non-zero central meridians.
Regards,
John