When I flush my toilet, the bowl fills almost completely (but does not overflow) before the water finally empties out. The bowl then refills to a normal level and stays there until I flush it again. All of the original contents of the bowl are flushed out, but it definitely requires much more water than expected to make that happen.
I'm wondering if the issue is with the toilet itself, or with the drain line. Replacing the toilet is simple and cheap enough, and that would be my first route. But I'm also wondering if the drain is partly blocked, causing water not to exit the toilet until a large volume has built up inside the bowl.
The house in question is a foreclosure and had been vacant for over a year, for what that's worth. It was apparently winterized prior to being abandoned (and they appear to have put antifreeze in the toilet bowl), but I have no guarantee that the winterization was done fully or properly.