Last few bottles are gushers?

This isn't a problem so much now, but a batch I made for my father in-law had this problem. A few months back I made a light lager. It sat in the primary for about a month, hit my FG, transfered to a secondary and lagered at high 30s for about a month. I bottled this batch like normal, 5 oz of corn sugar to 5 gallons. The sugar was disolved in boiling water and cooled then added to the bottling bucket at the beginning of the siphone, I did also add 1/4 - 1/2 pack of dry ale yeast to the bucket to make sure everything carbed up well.
I usually try a beer each week into aging to see how it's going. After week one the beer was a bit green and under carbed as expected. Week 2, I got a gusher which I really wasn't ready for. Both beers were from the end of the batch that I knew wouldn't be as clear and I might have gotten some trub so the plan was for them to be test subjects. I did open a second bottle out of the middle of one of cases and the carb level was about where it should be at 2 weeks.
Anyone have an explanation for this? I know it's not a fermentation problem and I doubt it could be an infection. I guess it could be the sugar didn't mix well, but adding it at the start of the transfer, like I always have, I doubt this is it either. If I can't nail this down I doubt I will give the beer to him even if I don't see any other gushers just because I would hate to get that dreaded phone call.

If you have any suspended solids in the bottle (trub, spices, whatever) they can form nucleation sites for the carbon dioxide bubbles. Lots of nucleation sites mean lots of bubbles mean gushers. I've had one in a spiced ale that I opened before all the spice settled out. That was the only one I've seen from the batch so far and half of them are gone now.

RM-MN said:

If you have any suspended solids in the bottle (trub, spices, whatever) they can form nucleation sites for the carbon dioxide bubbles. Lots of nucleation sites mean lots of bubbles mean gushers. I've had one in a spiced ale that I opened before all the spice settled out. That was the only one I've seen from the batch so far and half of them are gone now.

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I hope this is all the problem is, that would me that the issue should be isolated to the last few bottles then.