So you're saying there's a problem when you have close to 1500 object types in a project? How could you arrive at such a number even in a large, realistic project? The example you provided is obviously ridiculous with lots of redundant repetition, but does your project really have 1000+ unique object types with no redundancy?
The project bar needs an icon for every object type in the project, and with such a huge number eventually Windows, not Construct 2, fails to return any more icons. So there must be some internal limit in Windows. I don't know what else we could do about this, the project bar still needs to show those icons.