Thank you for your post.
There shouldn't be any issue with what you've mentioned and I've tried to replicate but wasn't able to.
I have a couple of quick questions to help us locate the issue:
1. Does this happen for all the windows in your model?
2. Does this happen in other models or just in your current one (i.e. if you open a new model can you replicate the issue)?
3. Has the wall(s) been exploded where the window(s) are located?
4. Does a message appear in the Ruby Console (go to Window > Ruby Console) when you replicate the issue? Please note that the Ruby Console must be open before you try to replicate the issue otherwise a message won't appear.
If anything appears in the Ruby Console, can you please copy and paste the message across to firstname.lastname@example.org
so we can have a further look into it?