I found a bug: "Include" filters -- filtering on tasks that contain a piece of text -- behave differently on Android & web than they do on Windows desktop, if you're filtering on multiple keywords.
On Android and web, filtering on Plan Vacation effectively searches for Plan OR Vacation, including all tasks that mention either word.
On Windows desktop, however, the logic is Plan AND Vacation, including only tasks that mention *both* words, though not necessarily in that order.
TickTick doesn't understand quotes or OR/AND keywords. For example, filtering on "Plan Vacation" (wrapped in quotes) simply requires a quote to appear in the task, it doesn't change the logic.