With Poster an odd thing happens when I title a post using only numerals.
In this case it was 1905 (the title of a film). I’m using Elixir’s Lunar theme and, after posting, a line of code appeared above the navigation bar (also visible in RW preview).
I’m attaching a screen shot showing the code: e.g. >905"> 905" /> etc.
If I enclose the title/numerals in quotes ("") the problem disappears. Adding text after the numerals, however, doesn’t fix it, it just adds the text to what is displayed above the navigation bar.
I’ve now corrected it on the live site by adding the quotes.
RW 8.4.1 - Stacks 4.0.3 - MacOS Catalina 10.15.2