using latest auto build didn't help. this happens only with a specific account.
# doveadm -o imapc_user=-----@domain.com -o imapc_password=---- backup -u =-----@domain.com -R imapc: dsync(----@domain.com): Panic: pool_data_stack_realloc(): stack frame changed dsync(----@domain.com): Error: Raw backtrace: /usr/lib/dovecot/libdovecot.so.0(+0x4209a) [0xb762b09a] -> /usr/lib/dovecot/libdovecot.so.0(default_fatal_handler+0x41) [0xb762b1a1] -> /usr/lib/dovecot/libdovecot.so.0(i_fatal+0) [0xb75fd99e] -> /usr/lib/dovecot/libdovecot.so.0(+0x547ce) [0xb763d7ce] -> /usr/lib/dovecot/libdovecot.so.0(+0x3ebf9) [0xb7627bf9] -> /usr/lib/dovecot/libdovecot.so.0(buffer_get_space_unsafe+0x78) [0xb7628658] -> /usr/lib/dovecot/libdovecot.so.0(buffer_append_space_unsafe+0x2a) [0xb762875a] -> /usr/lib/dovecot/libdovecot-storage.so.0(+0x60005) [0xb76dc005] -> /usr/lib/dovecot/libdovecot-storage.so.0(+0x62aa9) [0xb76deaa9] -> /usr/lib/dovecot/libdovecot-storage.so.0(+0x66e61) [0xb76e2e61] -> /usr/lib/dovecot/libdovecot-storage.so.0(imapc_connection_input_pending+0x14d) [0xb76e3a3d] -> /usr/lib/dovecot/libdovecot-storage.so.0(+0x67aac) [0xb76e3aac] -> /usr/lib/dovecot/libdovecot.so.0(io_loop_call_io+0x44) [0xb763a034] -> /usr/lib/dovecot/libdovecot.so.0(io_loop_handler_run+0xce) [0xb763ae8e] -> /usr/lib/dovecot/libdovecot.so.0(io_loop_run+0x40) [0xb76399d0] -> /usr/lib/dovecot/libdovecot-storage.so.0(imapc_client_run+0xa7) [0xb76e0297] -> /usr/lib/dovecot/libdovecot-storage.so.0(imapc_storage_run+0x26) [0xb76df1e6] -> /usr/lib/dovecot/libdovecot-storage.so.0(imapc_mailbox_sync_init+0x6de) [0xb76ddfde] -> /usr/lib/dovecot/libdovecot-storage.so.0(mailbox_sync_init+0x3b) [0xb76f468b] -> /usr/lib/dovecot/libdovecot-storage.so.0(mailbox_sync+0x3c) [0xb76f47cc] -> doveadm() [0x8072510] -> doveadm() [0x8072789] -> doveadm() [0x80729b2] -> doveadm(dsync_worker_msg_iter_next+0x29) [0x8070a69] -> doveadm() [0x806b6e1] -> doveadm() [0x806b736] -> doveadm(dsync_brain_msg_sync_more+0x4cb) [0x806bc7b] -> doveadm(dsync_brain_sync+0x3bb) [0x806a3ab] Aborted