Explorer slows down saving of Excel files

Anyone ever experience this? I did a bit of searching and read a few other posts with similar info without a solution to the problem.

The user can browse to the Excel file in Windows Explorer and then open it from the mapped network share. The user then makes changes to it and when is is saved takes 15 about seconds as opposed to 2 seconds with Windows Explorer closed.

Why the longer time saving with Windows Explorer open?

Thanks