Error on row deletion (partitioning by virtual column): Found a row in wrong partition

Scenario:

1. CREATE TABLE `t4` (

   `hour` tinyint(3) unsigned AS (HOUR(period)) VIRTUAL,

   `period` timestamp NOT NULL DEFAULT CURRENT_TIMESTAMP

   ) ENGINE=MyISAM DEFAULT CHARSET=utf8 PARTITION BY HASH (`hour`) PARTITIONS 24;

   insert into t4 select null, NOW() + INTERVAL RAND()*100 HOUR from seq_1_to_10000;

2. Repeat the following query:

   delete from t4 limit 1000;

   Actual result: Error: Found a row in wrong partition.