The issue is caused by 59a0236d commit.
The initial intention of the commit was to speed up
"mariabackup --prepare".

The call stack of binlog position reading is the following:
▾ trx_rseg_mem_restore
  ▾ trx_rseg_array_init
      ▾ trx_lists_init_at_db_start
            ▸ srv_start
Both trx_lists_init_at_db_start() and trx_rseg_mem_restore() contain
special cases for srv_operation == SRV_OPERATION_RESTORE condition, and
on this condition only rseg headers are read to parse binlog position.
Performance impact is not so big.

The solution is to revert 59a0236d.