Qt Assistant "with exact phrase" search does not work for phrases which starts with number followed by letter

The user wants to find some information on how the Qt SDK does handle 2D graphics. The user knows, the search with exact phrase can help him. By writing in the field "with exact phrase" phrases like "painting" will return headers which do contain the word "painting". The user now is trying to enter in this field the phrase "2D". The search returns nothing, even the previous search with the phrase "painting" returned the header, which does contain "2D Painting Example | Qt OpenGL ".

It can be easily reproduced with Qt Assistant.