Silicone cure times

I have noticed a very curious thing.  If I mix a bucket of silicone and pour it into the mould, then a few minutes later mix another lot of silicone in the same bucket, it takes on the cure time of the first mix - even if there is just a tiny bit of the first mix in the bottom of the bucket.
In other words, mixing fresh silicone in a bucket with silicone that has started to gel, seems to speed up the curing of the fresh silicone.
For example, last night I mixed a bucket of siilcone and poured it into the mould. No issues at all. Then about 15 minutes later (it was a warm evening) I poured some fresh silicone into the bucket I had used for the previous pour. (Remember ecoflex is supposed to have a pot life of 30 minutes).
As I mixed it, I immediately noticed lumps forming as it started to cure before my eyes and I started to panic. As a result I poured it straight into the mould quickly without waiting to degass it, and the end result was a baby full of bubbles that I have to pour again. ***sigh***
But I have noticed this phenomenon with other silicones too, psycho paint - if you top up the pot with fresh A & B even well before it has cured, the new fresh silicone cures at about the same rate as the remnants in the pot.
So just in case you notice your silicone curing far too fast, reflect if this might be a factor.