I contacted the Texas A&M plant answers, and was told that basically, if you have crepe myrtles, you have shoots. We cut down a crepe myrtle two years ago and I am still cutting off shoots, trying to pull shoots, and cursing shoots.
We tried spot-shooting with a broad-leaf weed killer with mixed results, and brown spots in our lawn. Some of the younger, tender shoots died; others just took a brief vacation and came back when we weren't looking.
I think we have found an occupation for our golden years--contending with crepe myrtle shoots!

aren't some of the variations less prone to do that?

we want to plant a Dynamite or Red Rocket in our front bed...BUT don't want to deal with shoots coming up all the time

does that happen if the plant reaches its max height or just any time

I've had six Miami, three Acoma, and a Centenial Spirit growing for 20 years here and have only noticed one root sprout coming up a couple of feet from the Acoma and that was recently. Gonna' pot it up and take to the plant swap.

They all have grown and bloomed wonderfully well. So I dunno' -- maybe it is my shallow black clay 'soil' that discourages them from sending up shoots.

Here is a link that might be useful: Crape myrtle varieties ...

Mine is the Natchez variety.