The best way to solve this issue is disable the save button in the IG and create a region button and submit the page which will refresh and reload the data.
You have found a fine solution. Some additional thoughts/info...
One problem in 5.1 is that there is no event that fires when the save has completed. In 5.1.1 there should be a interactivegridsave event that you could use.
To refresh the data in a grid you can do apex.region("staticid").refresh() but when you have master detail there can be many cached detail models. This would only refresh the detail model associated with the currently selected master. Before the save you could remember all the records that are changed and then after the save completes see if there is a corresponding detail model for each and call clearData (this causes a refresh) on that model.
Thanks very much John for additional information. knowing this will help me design the page accordingly.