Structure window's viewer-specific menu disappears when many sequences:one chain mappings are present

Noticed when working with alignments of repeat regions with Chimera, but also happens with ChimeraX.

Simple test:
>FER1_SPIOL/1-147
----MAATTTTMMGMATTFVPKPQAPPMMAALPSNTG-RSLFGLKT--GSRGGRMT-MAAYKVT
>FER1_SPIOL/1-147
LVTPTGNV
EFQCPDDVYILDAAEEEGIDLPYSCRAGSCSSCAGKLKTGSLNQDDQSFLDDDQIDEGWVLTCAAYPVSDVT
IETHKEEELTA-

Import and discover structures.
1. only one sequence gets the mapping to structure even though both could be (need a separate issue for this).
2. Use 3d-structure chooser again to map second sequence to existing structure view.

Problem: The Jmol/Chimera/ChimeraX menu is not shown, or if it was shown, it disappears after the second mapping is made.