Not always, but mine do that too. I usually snip below the roots and plant the new plant. The one you snipped it from will grow again. It's to the point now that I need to replant my tank because they are taking over.
Lol Now i know hwta the nameof the plants in the background are .I thought they were moneywort but they are bocopa ...and i have 1plant of hygrophila in there i might get somemore..