Alpha channel is pre-multiplied

I have customized the User0 channel in SP, setting its format to RGB8. Then, using a Filter created in SD, I have stored the four images I need in the R/G/B/A four channels of User0. However, when I export this User0 texture, the content of the Alpha channel is pre-multiplied onto the other channels, causing errors in the other channel information. I would like to ask if anyone has any good solutions.

The file format I used is TGA

Substance 3D Painter, version 8.3.0
Build 2094 - ef4d98e65d94c0756a3991957cab43f70b16c9b4