Hotbar selection changes if the "sign" is in the 9th slot

Steps to reproduce:

1. take signs(oak,..etc) from creative inventory.
2. put them in the 9th hotbar slot.
3. place 1 sign somewhere(optional: write text).

Observed results:

after the "sign" is placed, the 8th hotbar slot is selected.

 

NOTE:

No problems when using Mouse & Keyboard.

Only when using touchscreen this issue occours.