texture export failure

I was exporting textures from my project via standard UE functionality and some textures were exported not as .tga, but .t3d file with size 1-2Kb. I dont have any clue why, these texture were imported from .png and i see no difference to textures which are exported properly. I have never encountered this behaviour before. Does anybody have similar experience? Thanks.

Make sure you’re bulk exporting only images – if any other asset types get into the mix, I think you end up getting scene data spit out.

Yes, I am exporting only textures. It happens even if I use just export on selected texture, not bulk export on group of textures.