Explorer does not show some tiles that increase ukeire

[e00E]

Take the hand 123m12399p57s1122z .
The site says discarding 9p, 1z, 2z are equal with shanten 1, ukeire 8. and that "tiles that increase ukeire" is 0.
But after any of those discards drawing a 4s and discarding 7s increase ukeire because you can now advance the hand by drawing 3s and 6s instead of just 6s. Indeed if load 123m1239p457s1122z it does tell me that ukeire is now 12.