Just to let you know that right now I am changing the sources to behave much better with thousands of names. If you are interested, email me to adrian@tmssoftware.com with your registration email/code and I can send you a version to test as soon as it is ready. (probably by tomorrow).
It will probably fix this issue, but I am still not convinced having so many names is a good design choice, maybe you can use bigger ranges and refer to them in your app via the name and an index?
Say for example instead of defining:
Range0: A5
Range1: A6
Range2: A7
define just a Range02: A5:A7 and in your app use an index, say Range02.Top + index where index is from 0 to 2?
It of course depends in what you are exactly doing, which I am not really sure. I also don't know what you refer with adding a custom property to a range, if you can expand on that maybe I can offer you a better idea.