Comment 23 for bug 636720

In investigated a bit further:

In Ubuntu 10.04 (Lucid) the command
synclient -l
shows the option:
ClickFinger3 = 1

In Ubuntu 10.10 (default) the command
synclient -l
shows the option:
ClickFinger3 = 2

So Ubuntu 10.10 seems to suffer from exactly the same behaviour as Suse (for more information follow the link above).

man synaptics reveals the meaning of the ClickFinger3 option:
"Option "ClickFinger3" "integer"
    Which mouse button is reported when left-clicking with three fingers. Set to 0 to disable. Property: "Synaptics Click Action" "

From this, I conclude that by default, in Ubuntu 10.10, a left-clicking (?) with tree fingers is interpreted as a middle click.

Now - I had this issue when clicking with one finger, and I click the left (pysical) button.

Changing this option should not affect me at all, however if I set the option back to the original value (ClickFinger3 = 1) as suggested by Kruffwuff, then my problems are gone.