A few months back, I screwed up. I had a bucket of paint left over after my place was professionally repainted a few years back and decided to touch the place up by painting over some stains on the wall. I used a roller to paint approximately 3 m2 altogether.
Now there were several brown-black stains on the surface of the paint and it did smell funny (by which I mean slightly rancid), but it did not enter my mind that mould could grow in a bucket of paint - I just assumed the parts of the paint had separated and so I stirred the paint. The paint worked seemingly just fine after this and there is no discoloration.
After painting the wall (which is a concrete wall), it smelled a bit of what I now realise was mould, for about 30 minutes to an hour. After that however, there is no smell and no visible hint of mould on the wall.
I only now realised, after reading up, that indeed mould can grow in paint and that I accidentally painted with mouldy paint...
Should I still be worried about mould growing underneath or so? The apartment is usually dry as the desert and I have had no problems, there is no smell or discoloration whatsoever. Still...