I haven't seen anything like this, are you using a managed or referenced catalogue? Im not sure you should expect C1 to be able to filter based on a file state it may not know about until it touches each file, it would need to be continually checking which would lead to an overhead whenever it was running.
Is the read-only status real according to the file system?
Referenced. Happens with both Aperture referenced libraries imported into C1. As well as C1 importing directly from the folders into a new C1 library. There are certain JPEG files C1 simply does not like. Files that are fine in any number of other apps.
It knows the file state immediately. Probably when building previews. And it can't filter as there's no defined term for write only files. Which they are not at the file system level as I've successfully been able to re-save them in another app and try re importing the new file into C1. No joy. So I'm left with an unknown number of my better images that can't be viewed correctly and can't be exported correctly (tried).
The bigger issue is I can't find the tools in C1 that allow me to get my hands around those files. Aperture certainly provides those tools. They are important in maintaining a catalog/library over time. Without good filtering capability, one stumbles into them one by one. Usually at the worst moment. There's no shortage of iPhoto users who have no clue that images go missing in its library. My iPhoto library immediately got opened in Aperture, which has the tools, when Apple unified those libraries. C1 is similar to iPhoto in this respect.
For the price they want for C1, I had hoped for a more robust and capable catalog. Perhaps one reason why Sessions appears to be the more popular route amongst their long time pro users.