I can confirm this bug. Here are my findings:
If I access 2 array datums in the same action (i. e. set text to Array.At(0, 0) & newline & Array.At(0, 1) & newline), then I get this error. If I access them one by one, however, and add some text at the end, then it works normally (according to comments here, I guess it's because then it converts it into a string).
Here's the number I'm having problems with, but I see that some (not all) other numbers cause problems as well: 1909769338
capx: http://www.filedropper.com/c2arraybug
By the way, round() expression doesn't work here.