Several years back there were big problems with people putting up tents and sleeping in the park, washing in the water feature, going to the toilet on the nearby estate. The police used to be there every morning moving them on, the local councillors were involved and eventually it stopped. Worrying that it's starting to happen again.
The big green tent near the Coral St entrance is the BBQ stall, but Rambling Phil said that tents are in the opposite corner (Baylis Road/Waterloo Road junction), where they have appeared before. Probably because it's more tucked away.
It never stopped, there was just no tents. I often walk through the park and see people plotted, with suitcases, eating food, looking quite domestic. They never last long, I don't suppose the people there now with the orange tent will either. Think of it as a mini Sangatte. We're doing our bit.
To be honest, if they had means of waste disposal, then I wouldn't see a problem. It doesn't seem to bother the office workers and those that use the jerk chicken man (recommended), in fact, I think he employs a former park dweller, or at least he used to. A ragamuffin Pole, no less.