It is my understanding that Wordperfect's implementation has always worked well. That was the reason that Microsoft introduced the "feature" back in the '90s. It was done so they could say that they also had the feature.

There has been no release from MS that they have fixed it, AFAIK.

The work and pain involved in testing has kept me and probably many others from testing. Faithe Wempen wrote:"Since its inception, the Master Documents feature has been a bit quirky and buggy, and that fact hasn't changed with Word 2016, unfortunately." Microsoft Word 2016 In Depth