Are you saying that if you are using OneCore as your default synthesizer, if you create a profile for say, Word, which uses eSpeak, if you are using Word, and open an NVDA dialog (eg NVDA+control+g to change settings), NVDA then changes to OneCore while working in the NVDA dialog?  If so, that is expected - the profile is triggered by the current program - in this case, the program has changed to NVDA so it uses the configuration profile set for NVDA itself (the normal profile unless you've set an NVDA specific profile).  Similarly, in the same situation, if you alt+tab from one Word window to another word window (holding alt down long enough to show the alt+tab window) - the voice will revert to OneCore while reading that alt+tab dialog, as that is a different program, even though conceptually you are moving from one Microsoft Word window to another.