Mangled vertical centering of equations

I have had a recurring problem for years in LibreOffice writer where equations inserted with fn-F3 are not vertically centered. Sometimes the equation is centered on creation, but at some later time it becomes uncentered upwards, and all new fn-F3 equations are uncentered as well. An example is

https://github.com/skewray/skewray_2/blob/master/doc/9908-379b.odt

vs

https://github.com/skewray/skewray_2/blob/master/doc/9908-379.odt

The first is okay, but the second is mangled. I’ve tried playing with various frames that make up the equation table, but nothing seems to work except starting the entire document over from scratch.

I don’t think the problem is with the equation itself, though. The equation is well-centered inside its own ‘frame’, and that frame is vertically offset inside the table cell. So if I F11, select Frame, right-click, select Modify, and then change alignment from top to center, nothing changes.

There is also an object around the equation, which is identified as “Table Contents”. Same type of object as the equation numbering, which is centered. It appears to have no way to vertically center. There is a choice for paragraph vertical center, which does nothing. An image is at

https://github.com/skewray/skewray_2/blob/master/doc/image.png

Maybe there is a way to vertically center this object that is not obvious in the various menus?

https://bugs.documentfoundation.org/show_bug.cgi?id=98751