Why don't you start with all the forms hidden, and show only the one in the active tab?
Wysota is right - if a widget is hidden it will receive no update/resize events.

Whenever you select another tab you show the current form and hide the others.

And another thing: Do you update the contents of any widgets( list views, tables, etc ) in the forms somehow? From another thread or from the corresponding device(s) maybe?.

Because even if they are hidden or not their contents will be updated. This could have an impact on performance too.

How many widgets does one of those forms contains anyway? Are there many layouts involved( relayouting could take a long time on complex configurations )?

Regards