I think this is legal (though I can't quite remember the details).
Yes, this is legal, e.g.,
<B>foo bar &baz</B>
<B>foo bar {</B>
See clause 9.4.5 "Reference End" of ISO 8879:
[61] reference end = ( refc | RE ) ?
NOTE - ending a reference with an RE has the effect of suppressing
the record end.
The refc or RE can be omitted only if the reference is not followed
by a character that could occur in the reference, or by a character
that could be interpreted as the omitted reference end.
Glenn