Autodesk Revit comes packed with extra building and annotation tools including Windows, unfortunately in Revit 2015 the Windows do not work as they should, some flex but others break.
As part of the default installation, Revit loads a content pack of useful tools that can be added to your Revit building project as needed. These tools are found in the UK Content Library, that have well over 3500 extra Revit tools, across more than 400 directories subdivided into 41 category directories to help us find the content we need. One of these category directories is the normally, very useful Windows collection that has around 60 window families to choose from.
On the back of a tech support call we have recently learned that some windows, not all, produce weird effects when flexing Height and/or width parameters, such as the appearance of extra windows frames.
The fault lies in the family and this can be fixed by constraining the path of the sweep to the reference plane but if you need to do this for a lot of windows the quickest solution could be simply use windows from a previous version, such as 2014 for Revit or 2013 for Revit Lt.
We have informed Autodesk and after investigating they have confirmed that some windows have been created incorrectly and that the issue is logged with Autodesk Development team; we await news of any time scales for a fix to be released, but in the meantime:
Here is a short video outlining the family editing required: https://screencast.autodesk.com/main/details/b728f6b1-4c7e-4ee5-85b7-412c3b96e3ed
Or, if you do not have a previous versions of Revit, here is a link to an older UK Content Windows directory that you download and use:: http://a360.co/1pvwM5g
RECCOMENDATION: If you use an older version of the Revit windows you may want to just keep this somewhere accessible and dip into it when you come across a faulty 2015 window rather that replacing the directory.
Should you need any further help please contact Adris on 023 8086 8947.