I don't know exactly if it's a bug, but sometimes it can be a problem.
Scenario: I have a big (+3GB) ZIP file in a shared folder (\COMPUTER\file.zip). This ZIP file has a LOT of folders and files inside. I open the file in 7zfm, select 3 o 4 folders and right click the selection.
Result: 7zfm window hangs up, window goes white, and if I try to close it, windows tells me that it's not responding, givin the option to force close. Process explorer shows cpu and disk activity.
If I leave the program to run for 2 minutes, 7zfm returns to normal state and shows the menu.
Things that I've tested:
If I do the same thing directly from the computer storing the file, menu appears fastly (but not instantly), and it takes more time as I select more folders.
As more files are stores in the ZIP file, it takes longer.
Over saturated wifi network with slow speed, it takes more time.
I don't know what 7zip calculates when right clicking a folder, maybe you can speed this a little.