Unicode support for bidirectional languages is supposed to be implemented using the Unicode BiDi algorithm (UBA), detailed in http://www.unicode.org/reports/tr9/. Rule W5 states:

W5. A sequence of European terminators adjacent to European numbers changes to all European numbers.

It appears that QT do not implement this rule.

When typing in kate (verified to also happen in a QT application newly created with QT Creator) a sequence of Hebrew or Arabic letters, followed by a European Terminator (such as
the hash symbol - #), followed by a number, the ET should receive the level of the number.

logical order (upper case means RTL characters):

HELLO #12

UBA dictated visual order:

#12 OLLEH

Actual order performed by kate:

12# OLLEH

Sample test for you to test:

שלום #12