In the ovs-fields.7 manual page, the "MPLS Bottom of Stack Field" paragraph says:
"""
 * When mpls_bos is 1, there is another MPLS label following this one, so the Ethertype passed to pop_mpls should be an MPLS Ethertype. For example: table=0, dl_type=0x8847, mpls_bos=1,actions=pop_mpls:0x8847, goto_table:1"

 * When mpls_bos is 0, this MPLS label is the last one, so the Ethertype passed to pop_mpls should be a non-MPLS Ethertype such as IPv4. For example: table=1, dl_type=0x8847,mpls_bos=0, actions=pop_mpls:0x0800, goto_table:2
 """

The values 0 and 1 have been swapped: when BOS is 1, then no more label stack entries follows. Therefore, the manual page should say:
"""
 * When mpls_bos is 0, there is another MPLS label following this one, so the Ethertype passed to pop_mpls should be an MPLS Ethertype. For example: table=0, dl_type=0x8847, mpls_bos=0,actions=pop_mpls:0x8847, goto_table:1"

 * When mpls_bos is 1, this MPLS label is the last one, so the Ethertype passed to pop_mpls should be a non-MPLS Ethertype such as IPv4. For example: table=1, dl_type=0x8847,mpls_bos=1, actions=pop_mpls:0x0800, goto_table:2
"""

The problem was originally found on RHEL 8, but is also present in the latest git tree, currently at commit 89b522aee379 ("ovsdb-idl: Add function to reset min_index.").