When nesting progress bars in Jupyter lab where the second progress bar has leave=False, the second progress bar isn't fully deleted, and an empty div remains. This results in vertical space being added over time.

Here is a screenshot of the corresponding HTML. The first div in the list is the parent progress bar; the next five divs are empty leftovers for the sub-progress bar. The final div is for the --- line I printed to illustrate the vertical space.

I could reproduce this bug both in Jupyter 1.2.6 and 2.1.0. In both cases I had the current ipywidgets 7.5.1 installed. This bug is with both tqdm 4.43.0 and 4.45.0.

• I have marked all applicable categories:
  • exception-raising bug
  • visual output bug
  • documentation request (i.e. "X is missing from the documentation." If instead I want to ask "how to use X?" I understand [StackOverflow#tqdm] is more appropriate)
  • new feature request
• I have visited the [source website], and in particular
  read the [known issues]
• I have searched through the [issue tracker] for duplicates
• I have mentioned version numbers, operating system and
  environment, where applicable:

  >>>  import tqdm, sys
  >>>  print(tqdm.__version__, sys.version, sys.platform)
  4.45.0 3.7.3 (default, Mar 27 2019, 22:11:17)
  [GCC 7.3.0] linux