(Sorry for my bad English)
It seems PB reindex modified files only when the thought is activated or highlighted (by mouse over). This means the files that I opened from outside PB (e.g. Google Desktop Search) are not reindexed until I activate/highlight related thoughts in the Plex.
Add a pending_files.txt file in the installation folder of PB. The content of this file looks sometimes like this:
These paths are supposed to be added by the scripts/macros written by users. For example, in MS Word, users can write simple scripts that when a documents is saved or closed, add its path to pending_files.txt file.
When PB's main window is activated, PB will check pending_files.txt for new paths, then reindex corresponding files, then delete these paths from pending_files.txt.
In pending_files.txt file, if a path does not belong to any Brains, PB simply removes it; If a path does not belong to the current opened Brain, PB ignores it; Only the paths belong to the current opened Brain are processed.
This way, we should at least be able to keep the index for some of our documents (docx, xlsx, etc...) always up to date.