Kickstarter gets stuck/blocked?

[electric!sheep]

On my 1989 XT600, the kickstarter is getting "stuck" every few kicks. Here is what happens. I'll kick it through and WHAM it's like I hit TDC with no decompression. If I hit it mid-stroke, I need to let the kickstarter return before resuming. If I hit it at the top of the stroke, I need to sit on it for a while before it slips past.

1. I figured it was the decompression cable so I adjusted it, to no avail.
2. I then put pliers on the decompression lever and pulled it close as I kicked through. No improvement.
3. I then put a wrench on the rotor bolt and rotated counterclockwise while holding the decompression lever. Turns over just fine. Smooth when decompressed, hard when not, just as it should be.
4. I get the kickstarter stuck, turn over the engine as described above, and then retry the kickstarter. Still stuck.
5. Not sure about this, but sometimes it seems to turn over without a problem?

WTF is going on!?