OpenGL & Java Window resize problem


I have a C++ app that performed OpenGL drawing on a Java window with JNI. For some reason i have to save the backbuffer in a texture, i use glCopyTexSubImage2D. When I resize my window I call wglMakeCurrent and the app is locked during 1 or 2 second, but when i dont use glCopyTexSubImage2D there is no problem (no lock). Someone have information, idea ? (i dont want to use glCopyPixel, too slow…)