Deleting files in zip never completed

Hi all
i made a zip of a project folder using winzip
it was about 220Megs uncompressed and about 95M compressed

not sure how many files, maybe about 1000 in a few dozen folders including subfolders

later using Dopus i drilled down to folder i wanted to delete from the zip, hit the delete key, confirmed yes and then got a dialog box advising that it was removing the folder from the zip

i walked away as it was taking a while, came back an hour later and it was still doing 'something' - what ?
i finally had to kill it using task man

deleted the zip file because i didn't trust it anymore, remade with winzip but this time deleted the folders in winzip, it worked fine and pretty quickly too

is this a known issue w/ Dopus ?

I faintly remember some strange behavior with ZIP-files don´t finishing after 100% & then percentage falling back a bit & continuing etc., but i´m not sure if it was related to Opus. Can you otherwise reproduce that thing? e.g. deleting from other large ZIPs?