Character input for quick lump search is duplicated

[MrAlaux]

SLADE Version: 3.2.1
Operating System: Windows 7

Issue Details:
As the title says. However, the duplication does not happen right away.
For example, when typing "M", the program grabs it as such at first, and jumps to the first lump starting with that character. However, an instant afterwards, the input is duplicated for no apparent reason, so the program believes "MM" was typed instead. Such a thing does not happen on the text editor, and it is not related to the OS repeating the input when holding down the key, since the delay for that is much longer.