update step hangs up

Please, consider I'm a newbie.
I wrote a very simple transformation to update a single table column.
The table input step executes a SELECT like this one

SELECT TA.idimport, TB.idutente
FROM timp_log AS TA INNER JOIN st_utenti AS TB ON TB.utente=TA.utente

The output (update) step SET TA.idutente=TB.idutente, comparing idimport between TA and stream.

When I run it, this transformation hangs up.
(here a screenshot of the frozen transformation update_step_1.jpg)

But it runs good if I change TA.idimport with TA.* (more than 20 columns in table TA)
(here a screenshot of good execution update_step_2.jpg)

Sometimes, breaking the trasformation while in the hanging status, I get the following 'unexpected error'
update_step_3.jpg

There could it be anything bad of mine?
Can I do something to avoid this inconvenience?

My environment:
Windows7
PDI 4.4.0
MySql 5.1.41 MyISAM

Thanks in advance
Luciano

Attached Images

• update_step_1.jpg (24.0 KB)
• update_step_2.jpg (23.3 KB)
• update_step_3.jpg (38.7 KB)