How to increase the maximum character I can load in a string variable (e.g. in Set Flow Variable)?

Hi! I am using OO 10.70 I noticed that when the no. of characters i assign in my "Set Flow Variable" step reached around 63944... central stops adding but continue the flow to finish successfully. The result however is an incomplete set of text... Any idea on where I can change the setting if any? This scenario did not happen to me in my old version of OO 9.70 where I can write huge no. of characters and be able to use them completely... Rgds, Don