[Bug] Progress is not saved and page number not updated within resource when paging/scrolling in vertical mode (Japanese)

[russgrav]

Describe the bug

On the Test App, when I'm reading a Japanese book in vertical text mode, paging or scrolling through the current resource does not save the current progress or update the page number. This happens regardless of whether I'm viewing the book in paginated mode (where pages within a resource are flipped to via a vertical scroll gesture) or continuous/scroll mode (where you can scroll from left to right to advance the text). Progress is only saved and page numbers are only updated when I switch to the next resource/chapter. This also affects the bookmarking functionality, as bookmarks will just navigate me to the first page of the resource where that bookmark was added, rather than the page where I was last reading.

Note that this is not the case when reading books in Japanese in horizontal text mode, whether in scrolling or paginated mode.

This bug is similar to #556, but I wanted to add the additional context that progress is not being saved because of this issue as well.

How to reproduce?

Here's a video demonstrating the issue for paginated vertical EPUBs.

vertical-text-issue1.mp4

And here's the epub I'm using in the video: konosuba.epub.zip

Readium version

3.2.0

OS version

iOS 18.3.2

Testing device

iPhone 15 Pro Max

Environment

macOS: 15.3
platform: arm64
Xcode 16.3
Build version 16E140

Additional context

No response

[mickael-menu]

This is the same issue as #556, would you mind adding your additional information as a response to this original issue?