That's a "feature" of gmail's IMAP server that is easy to confuse for a client bug - see pugio's comment about having exact same problem when using Thunderbird.
Gmail knows nothing about folders (where given email is in exactly one of those), instead using "labels" (which an email can have zero or more of). Problematic "feature" here is that their IMAP interface exposes labels as folders. So, if client asks server to delete message from given folder, instead gmail removes label with that name (then adds "Archive" label, to confuse thing just that little bit more)
Luckily, there is an obscure "When a message is marked as deleted and expunged from the last visible IMAP folder" option to rectify this intentional defect.
That's a "feature" of gmail's IMAP server that is easy to confuse for a client bug - see pugio's comment about having exact same problem when using Thunderbird.
Gmail knows nothing about folders (where given email is in exactly one of those), instead using "labels" (which an email can have zero or more of). Problematic "feature" here is that their IMAP interface exposes labels as folders. So, if client asks server to delete message from given folder, instead gmail removes label with that name (then adds "Archive" label, to confuse thing just that little bit more)
Luckily, there is an obscure "When a message is marked as deleted and expunged from the last visible IMAP folder" option to rectify this intentional defect.