When exporting sections of a sequence as TGA sequence the frame numbers are kept the file name.
When exporting a TGA sequence in batches from the same sequence, the filenames currently reset at Filename_0000.TGA. It makes sense to keep the name of the frames being exported instead of starting at 0000 again. Current workaround is to export batches into seperate folders and then batch rename each set.

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Jason Lillebuen commented
Absolutely insane behaviour for an image sequence. Discovered this while trying to overcome a rendering issue nearing a deadline. Two suites utilized to render out an image sequence to save time, but they ended up OVERWRITING each others output because the first frame resets to zero? Seriously?
Do the people who write this software ever use it?! How on earth is this behaviour helpful or desired? No matter what part of your sequence you render, that frame is now frame zero? Why does this function differently than in After Effects?