It seems that the web UI treats spoilers without a space after ::: the same as the regular ones, while Thunder ignores those as spoilers. It looks like the closing spoiler marker may be entered without whitespace but it consumes extra text after the spoiler, and overall acts weird
I can create an issue if that’s needed, or this post may be referenced in an existing issue to be used as a test
:::spoiler no whitespace
Content
:::
::: spoiler whitespace present
Content
:::
:::spoiler one-liner no whitespace
Content:::
::: spoiler one-liner whitespace present
Content:::
Extra text in the end
::: spoiler one-liner whitespace present
Content
:::
Second extra text
produces
no whitespace
Content
whitespace present
Content
one-liner no whitespace
Content:::
one-liner whitespace present
Content:::
Extra text in the end
one-liner whitespace present
Content
Second extra text
1 point
