”tb22“ in markdown file, it raise exception

[dantezhu]

hi, when I use "tb22" in markdown file, it raise exception, like this.

An error occured. This is either a bug in UltiSnips or a bug in a
snippet definition. If you think this is a bug, please report it to
https://github.com/SirVer/ultisnips/issues/new
Please read and follow:
https://github.com/SirVer/ultisnips/blob/master/CONTRIBUTING.md#reproducing-bugs

Following is the full stack trace:
Traceback (most recent call last):
  File "/Users/nianyang.zhu/.vim/bundle/ultisnips/pythonx/UltiSnips/err_to_scratch_buffer.py", line 18, in wrapper
    return func(self, *args, **kwds)
  File "/Users/nianyang.zhu/.vim/bundle/ultisnips/pythonx/UltiSnips/snippet_manager.py", line 302, in expand_anon
    self._do_snippet(snip, before)
  File "/Users/nianyang.zhu/.vim/bundle/ultisnips/pythonx/UltiSnips/snippet_manager.py", line 779, in _do_snippet
    self._jump(JumpDirection.FORWARD)
  File "/Users/nianyang.zhu/.vim/bundle/ultisnips/pythonx/UltiSnips/snippet_manager.py", line 590, in _jump
    self._active_snippets[0].update_textobjects(vim_helper.buf)
  File "/Users/nianyang.zhu/.vim/bundle/ultisnips/pythonx/UltiSnips/text_objects/snippet_instance.py", line 100, in update_textobjects
    raise RuntimeError(
RuntimeError: The snippets content did not converge: Check for Cyclic dependencies or random strings in your snippet. You can use 'if not snip.c' to make sure to only expand random output once.