In a blog post released earlier today, Sony revealed that it would be using the PAL version of nine titles on the PlayStation Classic. The PAL versions will be included in the North American PlayStation Classic as well. Considering that North America televisions operate on the NTSC standard, the format difference could cause these games playing at different speeds or glitch out, rendering them unplayable.
https://www.notebookcheck.net/The-North-American-PlayStation-Classic-will-use-PAL-version-of-some-titles.369361.0.html