I have an Ultegra 10 speed group on my bike, and am having some issues shifting.

What works just fine:

• Shifting from smallest cog, all the way to the largest in 1 or 2 index click increments, exactly as it should.
• Shifting from a larger cog to a smaller cog, assuming I don't shift to larger than the 4th smallest cog or so, with a single index click.

However, if I go beyond the 4th cog, it will take 2 index clicks to begin to shift back towards the smallest cog.

Example:

If I shift all the way to the largest cog with 9 index clicks from the smallest (exactly as it should be), it will take me 2 index clicks to get it to move from the largest to the next cog. If I give it one more index click, it will move one more cog. At some point it will jump a cog (usually the 2nd or 3rd smallest) so that the final index click puts it back at the smallest cog.

This is definitely driving me crazy. Anyone have any ideas?