Thanks much for the June Reader update!
I installed the June version directly over the April version, and everything works fine: the installation went without hitch and the app is sticking fine after reboots. I'm not getting the Invalid Page error with previously opened books, either. (In fact, I don't think I've ever seen that error on the T1.) I've tested only epubs, though; I don't have any pdfs on my T1 at this moment.
The clock is a really nice addition, and I love that it updates only at a page turn (saves battery!). One small suggestion: Can you add an option to use a 24-hour format, and/or add AM/PM mark next to the (current) 12-hour format display?

I tried checking/unchecking the 24-hour format option in the main Date/Time Settings, but that doesn't seem to affect the in-reader clock. In fact I prefer the 12-hour format, but with AM/PM next to it. (Well I'm supposed to know AM/PM by the ambient lighting, but still...

)