Republicans block bills because they're stuffed full of unrelated things (by design - that way they can easily be painted as the bad guys - which is working, see your own comment). I'm not saying that the reverse doesn't happen - perhaps Democrats are okay with bloated bills, I dunno.
Good rule of thumb is when a bill is blocked by one party, go find out everything that's in it and what parts the blocking party objected to. I guarantee it won't be the stuff the bill is named after.