venue, the propriety of venue is fixed in the county chosen by the plaintiff. Tex.Civ.PRAC. & Rem.Code Ann. § 15.063 (Vernon 1986); Tex.R.Civ.P. 86-1. If a defendant objects to the plaintiffs venue choice and properly challenges that choice through a motion to transfer venue, the question of proper venue is raised. Tex.R.Civ.P. 86. The burden is on the plaintiff to prove that venue is maintainable in the county of suit. Id. 87-2(a). If the plaintiff fails to meet this burden, the trial court must transfer the lawsuit to another specified county of proper venue. Tex.Civ.PRAC. & Rem.Code Ann. § 15.063(1) (“The court ... shall transfer an action to another county of proper venue if ... the county in which the action is pending is not a proper county....”); Tieuel, 654 S.W.2d at 775 (<HOLDING>). If the plaintiff meets the burden, the trial
holding that if a modification petition is filed in a county where venue is appropriate it is improper to transfer the venue to another county merely because venue also would have been proper in the other county however once an enforcement proceeding is undertaken in an appropriate venue venue is improper in a different county over a subsequently filed petition to modify the decree which was the subject of the enforcement proceedings recognizing that the plaintiff has the right to file suit in any permissible county holding venue proper where proper when the action was commenced holding that even if venue was improper the case should have been transferred not dismissed recognizing that if the plaintiff files suit in a county where venue does not lie the plaintiff waives the right to choose and the defendant may have the suit transferred to a proper venue