The title change seems to have repurposed this bug. The original title
VisualEditor: Math formulas don't display correctly after save (until page is reloaded) was a dupe of bug 36060 a dependant of bug 51565.
The current title does not describe current behaviour:
With VisualEditor formulae editing beta feature OFF. Formula are displayed as PNG's and can't be edited.
With VisualEditor formulae editing beta feature ON. Formula are initially displayed as PNG's they can be edited. As soon as they are edited they switch to MathJax display but with very garbled output due to Bug 61497.