anto_next
Messages are usually not removed immediately when deleting them using IMAP.
Deleted messages are marked as deleted but can still be seen when using a Linux command line to view all messages in
/home/e-smith/files/users/username/Maildir/....
Email clients can be set to show or not show deleted messages, & to also remove deleted messages immediately, or remove them after so many days or remove them upon exit etc.
Most email clients will allow you to undelete a message that has been previously deleted, as long as that message has not been removed by any email client accessing the same mail folder.
Typically mobile devices may leave the messages deleted but not removed, & you can set how long the message will be retained before being removed eg a day, a week, a month etc.
So what you are seeing may be "normal" behaviour, it's just you are not aware of how IMAP mail really works when messages are deleted.
It sounds like you may have different settings for deletion/removal/purging in the different email clients you use, so you are seeing different behaviour between email clients when they access the same users message folders.
Take a look at some email messages on sme server using webmail, it will show you both undeleted & deleted messages, the deleted will have a line through them. There is an option to purge (totally remove) deleted messages.
This type of behaviour is normal in most database systems, where deleted means hidden (but still accessible if you undelete the record), & a further step of purging means the record "is really deleted".