Version: 1.5.2 (using KDE KDE 3.5.3) Installed from: Ubuntu Packages OS: Linux Please have a look at the screenshot. I marked the two problems in it. It is easy to see but takes a lot of words to describe ;-)
Created attachment 17110 [details] Watch how after 2006 follows 2 and the other counting-bug
Oh, I just noticed. There is actually a third bug in the picture! In the horizontal completion kspread is changing the algo while in the vertical it is not! So there is not only the "algo changing bug" but also "... but just in some cases".
Some of these problems seem to be caused by the fact that your text is not detected properly as a date value, so as far as KSpread is concerned, it is just a text, and thus it tries to find a sequence for a text, not for a date. Why does the result look so weird, that I don't know - the algo is ... strange.
Thank you for the bug report. As this report hasn't seen any changes in 5 years or more, we ask if you can please confirm that the issue still persists. If this bug is no longer persisting or relevant please change the status to resolved.