Bread-Bakers v107.n037.2

I frequently find that my homemade loaves have internal structure 
problems. The texture is good, and the crust is strong, but when cut 
into slices, the slices don't hold together - they tend to break into 
four roughly equal pieces pretty easily. I see this on both country 
white and whole wheat loaves, but not on every single loaf, and I'm 
not sure what the common thread is.

Do you know what could be causing this?

Thanks!