I have this odd situation in which I can write double subscripts in math mode in certain older TeXmacs files, but not in a new file.

 

Moreover, I can always write a letter-character as the second subscript, but a single math character does not show up. In other words, in math mode,

a_{x_i} (curly braces to show order of subscripts)

will display fine, but 

a_{x_1}

will not. 

Even more oddly, if I write a second math character, then both show up. So

a_{x_{12}}

will appear. If I then try to erase either of the math characters, they both disappear. They also continue to come in pairs.

Anyone have a similar experience?

Thanks in advance!

Michael