Getting crazy with "Left bar width" and editing

I've a site where I've fixed left bar width to 150px.

All pages start with a grid list in which I set left bar width to 150

In 2 of the pages I've editing data with popup when user click on a grid line.
In one page no problem: when user click on the grid ... editing comes out without problems and left bar remain 150px

In the other page: when user enter the page the first time all is OK ...

... but when user clicks on the grid line to open editing ... I see left bar move to default 300px

and remain to 300px ...

... till the user click on another link.
I looked everywhere to find left bar width settings for editing window but not able to find anything.
Any help?
Thanks a lot

Eros