Thanks for the comments. We understand that the functionality  the the touch screen changes when a screen reader is on (thank Joseph for the additional information) but that isn't really the main issue Even with the difference  in the way we interact with the touchscreen we should still be able to do certain interactions but we cannot. For example we know when NVDA is off we can simply tap or double tap an icon or button and  it will activate the expected response and when NVDA is on we also know that NVDA expects us to find the icon or button first, then double tap on the screen  to perform the associated function. However in some situations this doesn't work properly. Eg Programs pinned to the task bar cannot be opened when NVDA is on because the "find then double tap" method just does nothing. We just want to know whether other people have had this issue or have found a way around it.
We have managed to do extensive comparisons with NVDA on and off because I am a sighted user helping a blind user. The blind user has severe dexterity issues and needs to find away of using touch screen functionality only. At the moment these issues are making it difficult to use his computer. We appreciate, as Joseph Lee suggested, this might be a Microsoft problem rather than a NVDA issue, as we have just discovered that the similar issues occur with Microsoft Narrator.