[Dovecot] Dovecot upgrade from 1.2.x to 2.0.x: roundcube/squirrelmail sent folder doesn't work any more

[Gerhard Wiesinger]

Hello,

After upgrading from 1.2.x to 2.0.x I'm having problems using sent 
folder in Webmail applications like roundcube mail and squirrelmail.

Relevant config dovecot.conf:
mail_location = mbox:~:INBOX=/var/mail/%u

Different LIST behaviour from rawlog:
1.2.x: with Prefix ~/Mail
A002 LIST "" "~/Mail/sent"
* LIST (\NoInferiors \UnMarked) "/" "~/Mail/sent"
A002 OK List completed.

2.0.x: with Prefix ~/Mail
A0003 LIST "" ~/Mail/sent
A0003 OK List completed.:

Configured prefix for private spaces in roundcube mail is ~/Mail . 
Roundcube Webmail application checks for existence of the folder but 
dovecot doesn't return anything in 2.x.latest.

Is this by design?
Any ideas to fix it by configuration?
(I tried prefix Mail/ in roundcube mail without success)

Thunderbird works well.

Thnx.

Ciao,
Gerhard