Nested placeholder remains in output

[bra-fsn]

Describe the bug
We use colorful for coloring output for scripts started from Jenkins (using the https://github.com/jenkinsci/ansicolor-plugin plugin).
I'm not sure whether this is a bug or lack of support or both, but the effect is the following:
this line
logging.info(f"{colorful.bold_snow2(step.__name__)} starting")
produces the following ASCII output:
ESC[38;5;33m11:03:05ESC[0m ESC[38;5;68mINFOESC[0m ESC[38;5;75mworker_factory/mem:0B/473M/utime:0:ESC[0m ESC[38;5;253mESC[1mESC[38;5;231mDropNaESC[22mESC[39mESC[26m startingESC[0m
which is displayed in Jenkins output as (and you can see the output is truncated, instead of starting, there's sta:

It can be seen that an extra [26m (proportional spacing) is left, which can't be displayed (not supported?) by the Jenkins plugin. In the terminal this looks good.
After looking into colorful's code, I'm not sure if it's not a bug (the [26m is there is mark nested borders, but it's left there).

Environment and Version

• OS (incl. terminal and shell used): ubuntu:bionic docker image
• Python Version: 3.6.9
• colorful Version: the screenshot is with 0.4.2, but in the terminal I've tried with 0.5.4 which seems to produce the same output.

To Reproduce
https://gist.github.com/bra-fsn/5f875a29bf043ae74748f2f9b2dbac81

Expected behavior
I'm not sure, but I guess that [26m shouldn't be there.