JP2ECW, creation options PROJ and DATUM ineffective

[quickstuff@…]

When trying to assign a specific ERMapper projection/datum string to a JP2ECW file, the PROJ= and DATUM= creation options are ineffective.
The resulting jp2 file appears to have no projection info embedded.

E.g. (src.tif being any baseline tiff + tfw file):
"gdal_translate -of JP2ECW -co PROJ=GEODETIC -co DATUM=WGS84 src.tif dest.jp2"
"gdalinfo dest.jp2" does not report any projection. Close examination of the binary/hex contents of the file suggests that none gets written.

Of course I could rely on '-a_srs' to let GDAL internally assign the projection... but for backwards-compatibility with some applications, the ErMapper way of assigning a precise projection string is required.
By the way, the same creation options do work like a charm for ECW.
I use the last FWTools 1.2.3 under WinXP.

~Quentin S.