Weird. Reproducible bug.
Step 1. Edit a zh-tw page from a US IP.
Step 2. Save it. View the page. Spiffy.
Step 3. Click to the zh-tw page from the en page. OK.
Step 4. Leave it for a while.
Step 5. Click to the zh-tw page from the en page.
Nothing's there. Weird.
Step 6. Click on page history. Nothing's there either.
Step 7. Repeat Steps 1 through 6 as desired.
I'd say this is a pretty serious data loss problem.