Texture Manager Limitation

I can't seem to find much more info on roTextureManager, but is there a max number of bitmaps it can store? I'm using Texture manager to cache a list of images downloaded from urls. However, once I hit around 20 or so requests, the Texture request would start to fail (state = 4). The work around is to perform a cleanup() to the texture manager.

I was hoping texture manager can store more or I can set a max.

If the above assumption is false, what am I doing wrong?