I stumbled across a strange thing. I had Office 2013 installed on my computer running Windows 7 Professional.
I was using the Windows Classic theme.
When opening a particular template in Excel, quite a number of row heights had been changed, e.g. from 19 pixels to more than 400.
There was nothing I could do about it.
After some time of desperate trial and error, I changed to Windows 7 Basic theme, not really expecting any improvement, just for the purpose of having tried everything - and that made a difference!!!
After that, my spreadsheet behaved normally (no inadvertant change of row height).

I then changed back to Windows Classic as I like that better. This time, the strange spread sheet behaviour did not appear anymore.

Consequently, the theme itself doesn't seem to really have an effect on spreadsheet performance, but the process of changing themes seems to solve the problem somehow.

Does anybody have an explanation for that weird behaviour?

As the company I'm working for plans to roll out Office 2013 soon, any help preventing this issue would be greatly appreciated!

Thanks in advance!