In current Master builds, the Acc_description has disappeared from most standard controls such as Buttons, Checkboxes, Radio Buttons etc.

To compare:

1. Open LibreOffice 4.2.0. Focus lands on the Open File button.
Using NVDA, I press Insert+F1 and get this information:

Developer info for navigator object:
name: u'Open File'
role: ROLE_BUTTON
states: STATE_FOCUSABLE, STATE_FOCUSED
isFocusable: True
hasFocus: True
Python object: <NVDAObjects.Dynamic_SymphonyTextButtonIAccessible object at 0x05613B90>
Python class mro: (<class 'NVDAObjects.Dynamic_SymphonyTextButtonIAccessible'>, <class 'appModules.soffice.SymphonyText'>, <class 'NVDAObjects.IAccessible.Button'>, <class 'NVDAObjects.IAccessible.IAccessible'>, <class 'NVDAObjects.window.Window'>, <class 'NVDAObjects.behaviors.EditableText'>, <class 'editableText.EditableText'>, <class 'NVDAObjects.NVDAObject'>, <class 'baseObject.ScriptableObject'>, <class 'baseObject.AutoPropertyObject'>, <type 'object'>)
description: u'The Open a Document icon presents a file open dialog.'
location: (129, 193, 335, 59)
value: None
appModule: <'soffice' (appName u'soffice', process ID 3972) at address 5a0ed50>
appModule.productName: u'LibreOffice'
appModule.productVersion: u'4.2.0.4'
TextInfo: <class 'appModules.soffice.SymphonyTextInfo'>
windowHandle: 525122L
windowClassName: u'SALFRAME'
windowControlID: 0
windowStyle: 349110272
windowThreadID: 3540
windowText: u'LibreOffice'
displayText: u''
IAccessibleObject: <POINTER(IAccessible2) ptr=0xc84e81c at 57cf4e0>
IAccessibleChildID: 0
IAccessible event parameters: windowHandle=525122, objectID=-4, childID=-66
IAccessible accName: u'Open File'
IAccessible accRole: ROLE_SYSTEM_PUSHBUTTON
IAccessible accState: STATE_SYSTEM_FOCUSED, STATE_SYSTEM_FOCUSABLE, STATE_SYSTEM_VALID (1048580)
IAccessible accDescription: u'The Open a Document icon presents a file open dialog.'
IAccessible accValue: None
IAccessible2 windowHandle: 525122
IAccessible2 uniqueID: -66
IAccessible2 role: ROLE_SYSTEM_PUSHBUTTON
IAccessible2 states:  (0)
IAccessible2 attributes: exception: (-2147467259, 'Unspecified error', (None, None, None, 0, None))

The important line is:
IAccessible accDescription: u'The Open a Document icon presents a file open dialog.'

2. Now, open a current LibreOffice 4.3.0 dev build, any build from recent couple of days will do. The info looks almost identical for the same button, except:

IAccessible accDescription: u''

3. Back in LibreOffice 4.2, open any Writer document, then go to File/Export as PDF. All of the controls have explanatory descriptions, for example the "Tagged PDF checkbox":
Developer info for navigator object:
name: u'Tagged PDF'
role: ROLE_CHECKBOX
states: STATE_CHECKED, STATE_FOCUSABLE, STATE_FOCUSED
isFocusable: True
hasFocus: True
Python object: <appModules.soffice.SymphonyText object at 0x057EBA50>
Python class mro: (<class 'appModules.soffice.SymphonyText'>, <class 'NVDAObjects.IAccessible.IAccessible'>, <class 'NVDAObjects.window.Window'>, <class 'NVDAObjects.behaviors.EditableText'>, <class 'editableText.EditableText'>, <class 'NVDAObjects.NVDAObject'>, <class 'baseObject.ScriptableObject'>, <class 'baseObject.AutoPropertyObject'>, <type 'object'>)
description: u'Selects to write PDF tags. This can increase file size by huge amounts.'
location: (851, 419, 350, 25)
value: None
appModule: <'soffice' (appName u'soffice', process ID 3972) at address 5a0ed50>
appModule.productName: u'LibreOffice'
appModule.productVersion: u'4.2.0.4'
TextInfo: <class 'appModules.soffice.SymphonyTextInfo'>
windowHandle: 853040L
windowClassName: u'SALSUBFRAME'
windowControlID: 0
windowStyle: -1798569984
windowThreadID: 3540
windowText: u'PDF Options'
displayText: u''
IAccessibleObject: <POINTER(IAccessible2) ptr=0xc849c6c at 57cf3f0>
IAccessibleChildID: 0
IAccessible event parameters: windowHandle=853040, objectID=-4, childID=-673
IAccessible accName: u'Tagged PDF'
IAccessible accRole: ROLE_SYSTEM_CHECKBUTTON
IAccessible accState: STATE_SYSTEM_CHECKED, STATE_SYSTEM_FOCUSED, STATE_SYSTEM_FOCUSABLE, STATE_SYSTEM_VALID (1048596)
IAccessible accDescription: u'Selects to write PDF tags. This can increase file size by huge amounts.'
IAccessible accValue: None
IAccessible2 windowHandle: 853040
IAccessible2 uniqueID: -673
IAccessible2 role: ROLE_SYSTEM_CHECKBUTTON
IAccessible2 states:  (0)
IAccessible2 attributes: exception: (-2147467259, 'Unspecified error', (None, None, None, 0, None))

4. Performing the same in the LibreOffice-dev 4.3 build, I again get:

IAccessible accDescription: u''

This feels like some more general breakage to me. Note that this does not affect all descriptions. For example tables and table cells in Writer documents still expose the correct accessible description.