Fumes/vapour or steam from silicon or press?

[Ali P]

Hi Folks. I have been successfully printing straight sided European mugs for a while, but have had a go with some different mugs which have a lip at the top so need padding out in the press. I used my "spare" press (a second hand one that I had not used before) so I could set it up without adjusting the other one.
The mugs were each wrapped in a newly purchased piece of silicon so that the correct pressure could be applied. A vapour was evident whilst pressing - which does not happen with my other press.
The first mug came out with areas where it looked like the ink had blown past the border of the image at the top of the mug and had a spot of what I decided was probably water. The next mug was moved further down into the middle of the blanket but had a similar noticeable vapour. The vapour continued with each one, but the prints were better and conssitent with no blown areas.
My question is whether it is likely to be the silicon giving off fumes/vapour/steam as it is new?
(it does have a thick pen lines on - I made sure that was not in contact with the mug. As it had been supplied like that, I assumed it would not cause an issue.
Or would it just be because of the higher temperature and longer time? Or might it be from the press blanket itself?
I decided it couldn't be moisture as it surely would have been cleared after 4 presses!!
Any ideas?