This shouldn't happen, and I can't reproduce this problem on any of our test systems (including members of the Jurassic farm).
This is perhaps an issue with system typefaces. You can try editing the win.qss style sheet file. It is on the bin installation folder (C:\PCL\bin or C:\PCL64\bin by default).
Open win.qss with a good plain text editor; for example PixInsight's Script Editor. Search for the following text:
QTreeView#OBObjectTree QToolTip
It should be at line #259 if you haven't modified the original file. This entry determines the font face used to render tool tip messages for items of the Object Browser interface in the Script Editor, which is just what you're having trouble with. By default, this entry is:
QTreeView#OBObjectTree QToolTip {
font-family: DejaVu Sans Mono, Vera Sans Mono, Verdana, Courier, Monospace;
}
You can try something as:
QTreeView#OBObjectTree QToolTip {
font-family: Verdana, Courier, Monospace;
}
which should fix the issue in case your Windows XP is having problems to render DeJaVu fonts. You must exit/re-enter PI for the changes to take effect, or execute Preferences globally with the "Force style sheet update" option enabled (Style Sheet / Special GUI Effects section on the Preferences interface).
Let me know if this solves the problem.