If a formatting rule is used within the root indenting level of a numbered list, then the end of the formatting rule will create a newline, unless it's the last symbol in the message. The entry with the formatting rule will also create a new numbered list rather than continuing the old list.
What's at the beginning of this newline will not be treated as the beginning of a line for list formatting. For example,
**51. test**52. test
As can be seen by the bold entry restarting from 50, it's not treated as continuation of the first entry. Entry 52 has different indentation and so isn't treated as a list entry. Entry 53 is reset from 50, meaning it's treated as the beginning of a new numbered list.
To confirm the insertion of another newline where it's not needed:
The 2nd and 3rd indentation levels of numbered lists do not insert a newline when ending the formatting rule. However, it will still create weirdness, and is still treated as a new list. For example:
In here, the 4th entry is, for some reason, located at the second level instead of the third level. Removing the boldness from the previous entry corrects this.