Kettle Spoon logging not working properly (no details of errors shown).

Hi, I'm experimenting something weird with Spoon. Last week I was using Kettle 4.1 without problems, logging was working fine. Now I downloaded version 4.4 and logging seems to not work as It should. When I make a "Preview" for a tranformation and It has errors, log only shows that errors happened but with no details about the cause. For example:

2013/09/12 15:39:40 - Spoon - The transformation has finished!!
2013/09/12 15:41:14 - Spoon - Save as...
2013/09/12 15:41:14 - Spoon - Save file as...
2013/09/12 16:10:05 - Spoon - The transformation has finished!!
2013/09/12 16:10:27 - Transformation 1 - Dispatching started for transformation [Transformation 1]
2013/09/12 16:10:27 - Spoon - The transformation has finished!!
2013/09/12 16:10:27 - Transformation 1 - ERROR (version 4.4.0-stable, build 17588 from 2012-11-21 16.02.21 by buildguy) : Errors detected!
2013/09/12 16:10:28 - Transformation 1 - ERROR (version 4.4.0-stable, build 17588 from 2012-11-21 16.02.21 by buildguy) : Errors detected!
2013/09/12 16:10:28 - Transformation 1 - Transformation 1
2013/09/12 16:10:28 - Transformation 1 - Transformation 1

but sometimes it shows the detailed log, as next:

2013/09/12 16:13:38 - Spoon - Logging goes to file:///tmp/spoon_6e116eeb-1bdf-11e3-a7c2-27a466f466a5.log
2013/09/12 16:13:40 - class org.pentaho.agilebi.platform.JettyServer - WebServer.Log.CreateListener localhost:10000
2013/09/12 16:13:41 - Version checker - OK
2013/09/12 16:14:19 - Transformation 1 - Dispatching started for transformation [Transformation 1]
2013/09/12 16:14:19 - Get Variables.0 - ERROR (version 4.4.0-stable, build 17588 from 2012-11-21 16.02.21 by buildguy) : Unexpected error
2013/09/12 16:14:19 - Get Variables.0 - ERROR (version 4.4.0-stable, build 17588 from 2012-11-21 16.02.21 by buildguy) : org.pentaho.di.core.exception.KettleValueException:
2013/09/12 16:14:19 - Get Variables.0 - ERROR (version 4.4.0-stable, build 17588 from 2012-11-21 16.02.21 by buildguy) : sdf - : I can't convert the specified value to data type : 0
2013/09/12 16:14:19 - Get Variables.0 - ERROR (version 4.4.0-stable, build 17588 from 2012-11-21 16.02.21 by buildguy) :
2013/09/12 16:14:19 - Get Variables.0 - ERROR (version 4.4.0-stable, build 17588 from 2012-11-21 16.02.21 by buildguy) : at org.pentaho.di.core.row.ValueMeta.convertData(ValueMeta.java:3077)
2013/09/12 16:14:19 - Get Variables.0 - ERROR (version 4.4.0-stable, build 17588 from 2012-11-21 16.02.21 by buildguy) : at org.pentaho.di.trans.steps.getvariable.GetVariable.processRow(GetVariable.java:114)
2013/09/12 16:14:19 - Get Variables.0 - ERROR (version 4.4.0-stable, build 17588 from 2012-11-21 16.02.21 by buildguy) : at org.pentaho.di.trans.step.RunThread.run(RunThread.java:50)
2013/09/12 16:14:19 - Get Variables.0 - ERROR (version 4.4.0-stable, build 17588 from 2012-11-21 16.02.21 by buildguy) : at java.lang.Thread.run(Thread.java:724)
2013/09/12 16:14:19 - Get Variables.0 - Finished processing (I=0, O=0, R=1, W=0, U=0, E=1)
2013/09/12 16:14:19 - Spoon - The transformation has finished!!
2013/09/12 16:14:19 - Transformation 1 - ERROR (version 4.4.0-stable, build 17588 from 2012-11-21 16.02.21 by buildguy) : Errors detected!
2013/09/12 16:14:19 - Transformation 1 - ERROR (version 4.4.0-stable, build 17588 from 2012-11-21 16.02.21 by buildguy) : Errors detected!
2013/09/12 16:14:19 - Transformation 1 - Transformation 1
2013/09/12 16:14:19 - Transformation 1 - Transformation 1


According to what I've tried, detailed log is only shown the first time I run the preview. I mean, if I close Spoon and reopen it, and then do a preview, log seems to work fine. But if I do a second preview (even without changing anything in the transformation) I get a log like the first one pasted here, which says "Errors detected!" but says nothing about the cause.

Could it be a bug of version 4.4? Should I change some setting of kettle?

Hope there's a solution! Error logging is very helpful!