Comment # 11 on bug 959806 from Stakanov Schufter

This may be correct if you did set up: use different wallets for network and
local applications (in advanced). Since Wlan will be local but the pop/imap
server passwords of kmail are on the web, this will open up two different
password requests if the wallets are separated. 

For me it works now, just asks for the kde5 wallet password and stopped
"harassing" me with the migration passwords. At least for that user (which does
not have kmail/kontakt installed.