One cannot use more than 100 characters for a question poll : if you try it, you get an error message (because the maxlength attribute for the text input in posting_poll_body.html is higher, you can attempt it).

Instead of setting the maxlength attribute at 255, why not setting it at 100? After all, the maxlenght is set at 120 for subject in posting_editor.html (or 124 for replies).

Use that HTML code:

<input type="text" name="poll_title" id="poll_title" maxlength="100" value="{POLL_TITLE}" class="inputbox" />

instead of:

<input type="text" name="poll_title" id="poll_title" maxlength="255" value="{POLL_TITLE}" class="inputbox" />