Combining objects into union adds lines? *pics included

Hey, so I'm trying to get better with my lineard on animate cc, and I found that i can combine objects so i can actually use the paintbucket tool to fill without pulling my hair out. However, today i tried combining objects and the proggram seemed to add extra lines. Also, when i just tried using the paintbucket without the union step it seems to fill lines that aren't there, like its trying to fill the same shape as whats on the next frame? What is causing all this?