This might be of interest to you as to the reason the TIP (Tablet Input Panel) does not function within PB4:
Tablet PC Input Panel depends on an application's support for caret tracking. Input Panel uses caret tracking events to determine which text input control has focus and can invoke Input Panel. However, Input Panel does not appear when a caret is not present or if caret events are not being accurately generated. This paper describes some caret tracking best practices for enabling Tablet PC Input Panel that appears next to text entry areas in the application. The information in this paper pertains only to Input Panel when it appears next to a text entry area.
More info is available at:
customized Desktop PC (Haswell i7 4770 3.4 gHz with 32 GB RAM), Windows 10 Pro 64-bit, 256 GB SSD, and a Microsoft Surface Pro 2017, Windows 10, 512 GB SSD, 16 GB ram, i7