I need more concrete information.
can you explain the series of operations and options you set?
And also the .py files are needed to reproduce the problem.
actually, i found that if there are more than one window in gvim, this problem will appear
open a empty .py file, then in command mode, open the help file :h
then go back to the origin file and input:
now i can see a list, then input another char like
now the list disappears, but actually there are many items it can matched
now close the help window
and do the step 1 again, then the autocomplpopup script work perfectly
i tested in .py and .tex file, .tex file didn't have this problem