cannot strip branches and topics are messed up

[Uwe Brauer]

Hi

I don't know what happened but I am deeply worried.

Hg branches shows me 

year-20-21//alumnos:alumnos  482:b0a8e818ccec
english:version              481:3771e367e9bd
uwe                          223:34c12f88eb28
felix                        222:b98dcff146b5
ben                          221:5c8207491207
rebeca                       220:63826524614c
beamerarticle                 68:e897dea82c2e
year-20-21:alumnos           476:19a32e82bb17 (inactive)
english                      464:d103eb285181 (inactive)
year-20-21                   463:bbb47a192a97 (inactive)
default                      267:70f4576aa938 (inactive)

The branch year-20-21//alumnos:alumnos  482:b0a8e818ccec
is what worried me.

I had on the branch 
year-20-21 463:bbb47a192a97 (inactive)
the topic alumnos
year-20-21:alumnos           476:19a32e82bb17 (inactive)

But I don't understand why there is now a new branch
year-20-21//alumnos:alumnos  482:b0a8e818ccec

I just thought of stripping it 

Hg strip 482
but 

hg strip -r 482
abort: unknown revision 'year-20-21//alumnos'!


What shall I do. That happened once to me on a not very important
repository but this is serious. 

I cannot however present a recipe to reproduce the behavior.

In any case any help would be strongly appreciated.

Regards

Uwe Brauer