Lipo battery swelling

[Rcrcrus]

Hi all. I'm needing a bit of advice on 4 of my lipo's that started swelling this weekend while racing.
I give you a bit of history. I have just moved to South Africa after living and racing in the Uk for a few years. I am running a Losi truggy with CC mamba combo 2200 kv and Losi buggy with a tekin combo. All my lipos are 4s, over 30c and over 5000mah and have had no problem in the UK.
Under standing it is a lot hotter here on race days. Two weeks ago i ran the buggy no problem. But this weekend i ran the truggy and 4 of my packs swelled up (well feels like just the wrapping swelled up) When they had cooled down because they were rather warm, not to warm to hold. It just feels like lipo has swollen and gone back down and left the cooled heatsrink behind. When i got home i checked them on a balancer and each cell was only 0.01-0.02v out, I thought that was still quit good. I then charged them with no probs at all and checked on the balancer again and all came out good 4.19v-4.20v per cell on all 4 packs. I have read that swollen packs should not be used but mine are not any more they have gone down and left the wrapping behind. Can any one tell me if my lipos are still safe or what. Please ask if i have left any details out.
Cheers