Hyphen before <i> causes error message

[Richard Chonak]

While trying to reprocess some old GABC code with gregorio 5.2.1, I
found some unexpected behavior.

Placing a hyphen immediately before an "<i>" leads to gregorio aborting
with an error message.

$ cat a189517.gabc
name: March 30 sample;
%%
(c3)For(h)-<i>ev</i>(h)er(h)
$ gregorio a189517.gabc
997: in function `gregorio_rebuild_characters': assertion:encountered
repeated style
$ echo $?
1
$

Changing the hyphen to another character -- for example, an "x" -- makes
the error message go away.

Is this a known behavior?

--Richard