I had a look and this is a combination of two minor bugs which I’ve now fixed for the next release.
The first bug you can work around - it was resizing the texture before adding the border, and trying to be clever it was subtracting the border width/height from the size beforehand. The net result was that the input and output width/height are identical. This was a bug and I’ve now fixed it.
The other bug is that the border is not correctly choosing a width of 8 when compressing to PVRTC 2bpp, instead opting for the PVRTC 4bpp version - width 4.
I’ve been told by our lead PVRTC engineer that we may be overshooting with an 8x4 border anyway, so you should be able to work around the problems suitably by making the input texture sized 1024x1024 for now.
The next release should be available in about a month and a half - if you’d like I can provide an engineering drop with the fix though if you send an email to DevTech@imgtec.com.