In my current Small galaxy, Normal tech cost, Challenging difficulty game as the Terrans, I have completed the colony rush and am now thinking of invading the juicy planets of the minors. So, I looked up Planetory Invasion tech and saw that it took around 12 turns to complete with a cost of around 1200. After researching Soil Enrichment, I went to select planetory invasion, BUT...

The tech will now take 18 bloody turns to complete! Its cost is now shown as around 1800! What on earth is happening? And my research production has only increased in these few turns.

This is really upsetting me because Galactopedia also mentions the tech cost as 1200.