Subreport not showing the same output if called by main report

Hi all guys,

I have this main report (A4 portrait with a mono-record select) with some subreports. Please pay attention to the one with the red border

Here's a quick view of the subreport in the editor and a simple preview. Please note that results are displayed in 2 columns (correctly):



When I run my main report, the output is something like this:

As you can see, the result of my subreport is shown on just one column; and if  the subreport had more results, I wouldd obtain just a longer column which would hide the barcode below in the "third" section of the main report.

Am I missing something? Why does the subreport show a one-column result if I call it from the main report instead of the 2 column result I get running by itself?

PS: I'm using iReport 1.2.6 (I know it's old but i HAVE to)

Thanks in advance

Fabio