Memory leak when deleting texture

I use 2 large textures to put them onto the sphere. But there is a memory leak when I test it on SIS650 integrated chipset: I suppose texture memory is not freed when I call glDeleteTextures or destroy context. As a result I have a growing virtual memory size that is occupied by the application.
It is a potential problem for me because I create and destroy these OpenGL-enable windows many times.
The problem eliminates only when I bind both textures onto the primitive at least one time.
Is this a SIS bug? I tried this on NVidia chipset-based cards, no bugs persisted.

Just some more words: I make these under win32.

Nvidias HW is cake when working with textures. A lot of approaches works when Intel, SIS, Ati is showing bugs. So if you want to check is your approach (even if it match GL spec) valid check it on Ati (Intel, SIS) & if there is no bug it’ll work everywhere.