Edit Mode broken when addon is enabled

[fs2597]

Describe the problem

Edit Mode is broken when this addon is enabled. The Edit Mode frame is messed up (wrong height, stuff overflowing), some movable placeholders (blue boxes) are missing, and an error pops up in BugSack.

Fixed by adding this:

BuffFrame.numHideableBuffs = 0

What steps will reproduce the problem?

1. Press Esc to open the Game Menu
2. Click the button to go into Edit Mode

Consider attaching a screenshot below to help describe your issue (Attach directly, do not link to other websites)

What version of the addon are you using? (Stating 'latest' is not useful)

v11.0.1

Do you have an error log of what happened?

Interface/AddOns/Blizzard_BuffFrame/Mainline/BuffFrame.lua:390: attempt to compare number with nil

Going into edit mode calls this:
https://www.townlong-yak.com/framexml/live/Blizzard_BuffFrame/BuffFrame.lua#390

function BuffFrameMixin:RefreshCollapseExpandButtonState()
	self.CollapseAndExpandButton:SetShown(self.numHideableBuffs > 0);

but numHideableBuffs only gets set here:
https://www.townlong-yak.com/framexml/live/Blizzard_BuffFrame/BuffFrame.lua#408

function BuffFrameMixin:UpdatePlayerBuffs()
	self.numHideableBuffs = 0;

which never gets called when all the events on the BuffFrame are unregistered.

Any additional information? (example: WoW language if not English)