When multiple custom indexers are used, increment updates pass the wrong files

[randym32]

Background
I have a project with two different, custom source indexers. Each is given a different starting path and file extension to index files over. The full index works as expected.

However, an incremental index does not work as expected. The indexer(s) are called with the wrong kind of file, from the folder that does not go with the indexer.

[mainjak]

how solve it?