iCloud syncing -- how does it work?

I keep a daily record of my weight in Numbers. I make entries on my iPhone, iPad or iMac depending on where I am at the moment. Today I opened the iPad to this document and found about ten days of recent entries were not there. I opened the iPhone copy and saw that the missing entries were there, but in the next few seconds they disappeared, as the two copies were synced the wrong way. Is that normal? If so, how can it be avoided? If I can't avoid it, how can I reverse it?