Hi,
The following bug exists in Dread Lords (1.5), and (1.4) not tested the other versions, and I would bet that the bug
also exists in the expansions:
When a planetary improvement will be finished next turn and the build queue is otherwise empty, ending the turn will result in the improvement to be build (so far no bug), but will cost nothing. This means ie. if a Marketplace is build on a planet in one turn and it has nothing else in the build queue, building the Marketplace does cost nothing!- This is also true for all other planetary improvements.

The cause seems to be that the tax and upkeep calculation seems to be done after the building of planetary improvements on each turn (and not keeping track how many hammers were used...). Such a bug does for obvious reasons not exist with research and military production. Considering the cause the bugs seems to have been introduced with the patch (or surfaced with it) that introduced the change that remaining social production is no longer wasted...

I think it would help the developers if anyone, I do not have the expansions, tests whether the bug holds also in the
other expansions. Easy test scenario is as follows: Start a new game set the production slider to 100% and the social production slider also to 100% and build a factory on the homeworld (no focus or focus on social production). End the turn (do nothing else). Your treasury will have fallen below 5000, look at the tax screen (maybe two times, with ie. the research screen in between) and you will see that your treasury should fall in the following turn also. Press next turn again (again do nothing else). And look whether the treasury did increase by the amount given now by the tax report screen (you should not see any expenses for social production on that report), if it did rise by that amount the bug also exists in that expansion.