Everything started re-indexing again now. This was never happening with official sources.
(It does happen with *my* sources, because git updates timestamps on all files, and MacPorts thinks that all ports are changed, and I just do not know how to fix this annoying behavior, but at least my sources are a) my problem, after all, and b) re-indexing 500 ports is fine – but not 40k+.) On slower hardware re-indexing everything translated in a multi-hour time-waste. And I do not only mean G4 machines. My modern, but using a slow SD card, RISC-V tablet takes forever to index all ports, far longer than a PowerMac.