I've noticed this with my Outlook Express under XP.
When I use either Quicken 2009 or TurboTax, the icons on my Outlook Express toolbar change.
I normally have them as "small icons". But after using Quicken or Turbotax, the icons are BIG and shifted across the toolbar line such that my "Send/Receive" icon is no longer present.
I seem to recall a DLL for these toolbar functions, and am guessing that Quicken loads a version that says "big icons", and Turbotax loads yet another DLL that says "huge icons".