Bug #82020 table lost or missing when alter column

Description:
I was trying to use workbench to change a column Collation from "Table Default" to "utf8mb4 - default collation", and after "Synchronize Model...", there's an error reported. I didn't see the error throughly.

However, after I close the Synch wizard, the table "party_relationship" has gone!!!

This happened in the production environment. And it's really a core table. We cannot lost it!

Meanwhile, this also appeared in DEV. I don't do any change in PROD and really hope someone could please help me to recover the data back.

After tried in DEV, I cannot create the same table name in the database. Also in dbname folder I cannot find the party_relationship.frm or party_relationship.ibd. All other tables can be found. And there are #sql2-6bbe-1369f.frm and #sql2-6bbe-1369f.ibd.

Please is there anyone could tell me if we can recover the table from the #sql2* files?

How to repeat:
I've no idea

I also got the error message from the log file:
2016-06-27 19:55:54 1008 [ERROR] InnoDB: dict_load_foreigns() returned 38 for ALTER TABLE `piao`.`party_relationship` 
ADD COLUMN `PARTY_NAME_FROM` VARCHAR(100) NULL DEFAULT NULL AFTER `PARTY_ID_TO`
2016-06-27 20:04:57 7fd52cd0d700  InnoDB: Error: in ALTER TABLE `piao`.`party_relationship`
InnoDB: has or is referenced in foreign key constraints
InnoDB: which are not compatible with the new table definition.
2016-06-27 20:04:57 7fd52cd0d700  InnoDB: Error: in ALTER TABLE `piao`.`party_relationship`
InnoDB: has or is referenced in foreign key constraints

Since I was using workbench to model, why there is foreign key issue please?

Today after table missing and could not simply create table since foreign key constraint, I drop foreign key constraint.

Again, I get some error when trying to create new party_relationship table. And lost Connection when I try to query the table. I will attach log information which said this may be a bug.

Please provide a repeatable test case otherwise we aren't able to repeat just with your description. Thanks in advance.