JPEG 2000 for Pascal project is based on OpenJpeg library. For a very long time there was a bug that caused alpha (fourth and subsequent image channels) channel to be saved with all the samples having the value of 0.5 (128 for 8bit channels). This buggy behavior also depended on compiler settings - optimization level in case of GCC. You could use at most O1 in Windows and Linux, and only O0 in Mac OS X. Bug was also present when compiling with C++ Builder (to get object files usable in Delphi) but only when irreversible DWT transformation was enabled in OpenJpeg during encoding (it wasn't before, but working versions of both PasJpeg2000 and Imaging use it now when lossy compression is selected by user to get smaller files).
You can read more about it in this news group post. Basically it was all fixed by changing a condition in one if statement to prevent accessing the fourth element of a three element array.

So what can you expect in the next version of PasJpeg2000 library?
Higher GCC optimization levels should make it a lot faster when using Free Pascal (particularly in Mac OS X where O0 was used). Irreversible DWT transformation produces smaller lossy files than current PasJpeg2000 version and with optional MCT (multicomponent transform - basically RGB>YCbCr) you get even smaller ones. There's now also a patch that enables OpenJpeg to get palettes from JP2 files so indexed JPEG 2000 images could be supported too. And finally, there are some bug fixes (wrong reconstruction of subsampled files, ...).