if create a pipeline as 
appsrc ! gleffects ! glimagesink 

but didn't push buffer fast enough (slower than caps's FPS), gl render window only redraw a few frames, and then stay at last frame.  but if triggered some UI exposed event (move ,resize ,or other window overlay gl render window), some frames updates ,then stay again. 

but this problem only happend on windows. linux works OK

if pipeline is 
appsrc ! glimagesink 
no such problem. (both windows and linux worked)


after some debug, I found 
_gst_gl_upload_perform_with_data_unlocked
use pointer compare 
 upload->in_tex[i]->data != data[i]
to determine if glmemory needs to be re-upload ,I'm not sure if this is incorrect,
in pipeline appsrc ! gleffects ! glimagesink  
these two pointer almost equals every time on windows ,but different every time on Linux. 

if without this condition check , problem gone.