Just updated to -ubuntu18 and I'm still having the issue.

Here's the shell output:

jon@tiny:~$ kmail --nofork
ASSERT: "account" in /build/buildd/kdepim-3.5.6/./kmail/kmailicalifaceimpl.cpp (1478)
WeaverThreadLogger: thread (ID: 1) suspended.
WeaverThreadLogger: thread (ID: 2) suspended.
WeaverThreadLogger: thread (ID: 3) suspended.
WeaverThreadLogger: thread (ID: 4) suspended.
kdecore (KAction): WARNING: KAction::plugAccel(): call to deprecated action.
kdecore (KAction): WARNING: KAction::plugAccel( kacc = 0x8224d88 ): KAccel object already contains an action name "move_message_to_folder"
kdecore (KAction): WARNING: KAction::plugAccel(): call to deprecated action.
kdecore (KAction): WARNING: KAction::plugAccel( kacc = 0x8224d88 ): KAccel object already contains an action name "copy_message_to_folder"
kdecore (KAction): WARNING: KAction::plugAccel(): call to deprecated action.
kdecore (KAction): WARNING: KAction::plugAccel( kacc = 0x8224d88 ): KAccel object already contains an action name "jump_to_folder"
kdecore (KAction): WARNING: KAction::plugAccel(): call to deprecated action.
kdecore (KAction): WARNING: KAction::plugAccel( kacc = 0x8224d88 ): KAccel object already contains an action name "remove_duplicate_messages"
kdecore (KAction): WARNING: KAction::plugAccel(): call to deprecated action.
kdecore (KAction): WARNING: KAction::plugAccel( kacc = 0x8224d88 ): KAccel object already contains an action name "cancel"
kdecore (KAction): WARNING: KAction::plugAccel(): call to deprecated action.
kdecore (KAction): WARNING: KAction::plugAccel( kacc = 0x8224d88 ): KAccel object already contains an action name "inc_current_folder"
kdecore (KAction): WARNING: KAction::plugAccel(): call to deprecated action.
kdecore (KAction): WARNING: KAction::plugAccel( kacc = 0x8224d88 ): KAccel object already contains an action name "dec_current_folder"
kdecore (KAction): WARNING: KAction::plugAccel(): call to deprecated action.
kdecore (KAction): WARNING: KAction::plugAccel( kacc = 0x8224d88 ): KAccel object already contains an action name "select_current_folder"
kdecore (KAction): WARNING: KAction::plugAccel(): call to deprecated action.
kdecore (KAction): WARNING: KAction::plugAccel( kacc = 0x8224d88 ): KAccel object already contains an action name "inc_current_message"
kdecore (KAction): WARNING: KAction::plugAccel(): call to deprecated action.
kdecore (KAction): WARNING: KAction::plugAccel( kacc = 0x8224d88 ): KAccel object already contains an action name "dec_current_message"
kdecore (KAction): WARNING: KAction::plugAccel(): call to deprecated action.
kdecore (KAction): WARNING: KAction::plugAccel( kacc = 0x8224d88 ): KAccel object already contains an action name "select_current_message"
kdecore (KAction): WARNING: KAction::plugAccel(): call to deprecated action.
kdecore (KAction): WARNING: KAction::plugAccel( kacc = 0x8224d88 ): KAccel object already contains an action name "delete"
kdecore (KAction): WARNING: KAction::plugAccel(): call to deprecated action.
kdecore (KAction): WARNING: KAction::plugAccel( kacc = 0x8224d88 ): KAccel object already contains an action name "edit"
kdecore (KAction): WARNING: KAction::plugAccel(): call to deprecated action.
kdecore (KAction): WARNING: KAction::plugAccel( kacc = 0x8224d88 ): KAccel object already contains an action name "use_template"
kdecore (KAction): WARNING: KAction::plugAccel(): call to deprecated action.
kdecore (KAction): WARNING: KAction::plugAccel( kacc = 0x8224d88 ): KAccel object already contains an action name "display_message"
Weaver dtor: destroying inventory.
WeaverThreadLogger: thread (ID: 1) destroyed.
WeaverThreadLogger: thread (ID: 2) destroyed.
WeaverThreadLogger: thread (ID: 3) destroyed.
WeaverThreadLogger: thread (ID: 4) destroyed.
Weaver dtor: done