This plant has a tendency to do this, here a quote I picked up while doing a quick search:
In my tank this plant has grown about 21 inches and then 12 inches out of the water apparently if you trim the aquatic leaves just below the surface the plant will stay smaller and aquatic. Aquatic leaves are slender and pointed whereas emerged leaves are more round.
Depends on the Echinodorus sp, some do some don't.. Spraying in a living room invironment under artificial light wont make much of a difference. It evaporates again before it has the chance of doing any good.. Than you would realy need a closed system with a hood to keep the air humidity at steady levels. So it's kinda trail and error to find a sp. that aint to fussy about lower air humidities.
Seeing the aboved picture, if that is a E. palaefolius it already answers the question i guess.. Personaly i have the Jungle star cultivar from Dennerle growing like this, it also stands in a pot in the living room and holds on pretty good. Seem more Echinodorus like this, but didn't found out with sp they were.